A lonely woman (Barbara Cook) longs for a child of her very own. One day, a good witch gives her a barley corn to plant, and the next day the flower blooms, revealing a beautiful young girl "no bigger than her thumb." (Jodi Benson) The woman names her Thumbelina. Thumbelina spends time with her mother's farm animals but is worried that there is no one around of her own size ("Thumbelina"). One night, her mother tells her a story about fairies. After being put to bed, Thumbelina imagines that someday she will be able to find someone to love ("Soon"). As she is humming to herself, Prince Cornelius of the Fairies (Gary Imhoff) flies by her windowsill and is enchanted by her. The two take a ride on Cornelius' bumblebee, during which they fall in love ("Let Me Be Your Wings"). During this ride, a toad named Grundel (Joe Lynch) sees Thumbelina and declares to his lovely mother Mrs. Toad (Charo) that he loves her.
Cornelius returns Thumbelina to her windowsill and promises to come back for her the next day. After he leaves, Thumbelina goes to sleep in her walnut bed and is kidnapped by the beautiful and very sexy Mrs. Toad. When Thumbelina awakes the next morning, she is on a lily-pad far away from home. Mrs. Toad declares that Thumbelina will join their family singing troupe "Singers de Espana" (counting Grundel's brothers, Mozo and Gringo) and that Thumbelina will also marry Grundel ("On the Road"). The group leaves her alone on the lily-pad to fetch the priest, despite her protests. Thumbelina's cries for help are heard by Jacquimo (Gino Conforti), who helps her free of the lily-pad and encourages her to follow her heart and find her way home to her mother ("Follow Your Heart"). Jacquimo himself promises to find Cornelius, who lives in the Vale of the Fairies. Meanwhile, Cornelius has learned of Thumbelina's kidnapping and goes searching for her.
Thumbelina almost reaches home, but she is stopped by Berkeley Beetle (Gilbert Gottfried) who wants her to join his act at the Beetle Ball. Thumbelina is forced to perform at the Beetle Ball, but at the end is kicked out for being "too ugly" (as those beetles only like the appearances of beetles). ("You're Beautiful, Baby") Grundel, who is also searching for Thumbelina, tracks down Beetle and forces him (by taking his wings) to help find Thumbelina. Searching for the Vale of the Fairies, Jacquimo seeks help from a fleeing rabbit and its pursuer, a fox. The fox angrily shoves him out of the way and a strong gust of wind blows the swallow into a tree, driving a thorn through his wing. When the cold winter frost arrives, he becomes too weak to fly to the point that he loses consciousness and falls to the ground. The falling snow also causes Cornelius to fall from his bumblebee into a pond, where he is frozen in ice. Beetle finds Cornelius and cuts out a block of ice in which the Fairy Prince is trapped to bring to Grundel. Elsewhere, Thumbelina's mother can only wait at home and hope for the best ("Soon (Reprise)").
With both Cornelius and Jacquimo incapacitated, Thumbelina takes shelter from the winter frost in a shoe. She is rescued by the beautiful and very sexy Ms. Fieldmouse (Carol Channing) who tells her that Cornelius is dead. She convinces a heartbroken Thumbelina to join her to visit Mr. Mole (John Hurt), where Thumbelina is told to sing for him. They take a walk in Mr. Mole's extensive tunnels, where Thumbelina discovers the unconscious Jacquimo. Mr. Mole tells Ms. Fieldmouse that he would like to marry Thumbelina, and she agrees to convince Thumbelina that it would be for the best ("Marry the Mole"). Grundel learns that Thumbelina is to marry Mr. Mole and abandons the frozen Cornelius with Beetle, allowing three young jitterbug children that Thumbelina befriended to light a fire to melt the ice that has trapped Cornelius. Thumbelina sneaks out of Ms. Fieldmouse's home to visit Jacquimo. He wakes, and Thumbelina removes the thorn from his wing. Before she can explain that Cornelius is "dead", Jacquimo flies off, still determined to find the Vale of the Fairies.
When Thumbelina is prompted by the minister at the wedding ceremony, she responds that she cannot marry Mr. Mole, eventually leading into a chase by Beetle, Grundel, and the others. However, Cornelius and the jitterbug children arrive to stop them and Cornelius engages Grundel. Despite his efforts in stalling the crowd long enough to secure Thumbelina's escape, the battle eventually culminates in both he and Grundel falling into a bottomless pit. Thumbelina manages to scare her pursuers by causing a mountain of jewelry to slide toward them, and she escapes to the surface, where she is found by Jacquimo, who says that he has found the Vale of the Fairies. They fly there, and after Thumbelina sings ("Let Me Be Your Wings (Reprise)"), the ice thaws and Cornelius, who survived the fall and is still with the jitterbug children, appears to be reunited with his love. Cornelius proposes Thumbelina accepts, the pair kiss and wings sprout from Thumbelina's back. The wedding is celebrated with Thumbelina's mother, Jacquimo, the jitterbug children, and Cornelius' family in attendance.
Screenshots during the credits reveal that Beetle resumed his normal, pop star life and got his wings back; Grundel survived the fall with a broken leg and married a female toad; Mr. Mole married Ms. Fieldmouse, and the rabbit and fox Jacquimo tried to ask for help ultimately found friendship.
- Jodi Benson as Thumbelina - The main protagonist of the film.
- Gary Imhoff as Prince Cornelius - The Prince of the Fairies and Thumbelina's love. He is the tritagonist.
- John Hurt as Mr. Mole - A fabulously wealthy but self-involved and cynical rodent who marries Ms. Fieldmouse at the end of the movie. He is the main antagonist
- Joe Lynch as Grundel - The oldest son of Mrs. Toad and the secondary antagonist of the film. When he first sees Thumbelina flying with Cornelius, he instantly falls in love with her and becomes hell-bent on marrying her.
- Carol Channing as Ms. Fieldmouse - A rather greedy yet kind, caring, unbearably beautiful and insanely sexy field mouse who takes Thumbelina in from the cold and persuades her to marry Mr. Mole. She is the tertiary antagonist
- Gilbert Gottfried/Randy Crenshaw (singing) as Berkeley Beetle - A pop star beetle who owns his own "beetle band" and a so-called "connoisseur of sweet nectars, a fancier of fine threads and judge of beautiful women."
- Barbara Cook as Mother - The widow who mothers Thumbelina since her birth from a flower.
- Gino Conforti as Jacquimo - A wise swallow who speaks with a French accent. He is both the narrator and the deuteragonist.
- Will Ryan as Hero / Reverend Rat. The hero is the widow's guard dog, who is a friend to her and Thumbelina. The Reverend Rat tried to marry Mr. Mole to Thumbelina.
- June Foray as Queen Tabitha - Cornelius's mother and Queen of the Fairies
- Kenneth Mars as King Colbert - Cornelius's father and King of the Fairies
- Charo as Mrs. Toad - A sexy, gorgeous and famous Spanish singer and mother to her three sons Mozo, Gringo, and Grundel.
- Danny Mann as Mozo Toad - The youngest son of Mrs. Toad
- Loren Lester as Gringo Toad - The middle child of Mrs. Toad
- Michael Nunes as Li'l Bee, Tawny Sunshine Glover as Gnatty, and Kendall Cunningham as Baby Bug - Three young jitterbugs, all of whom Thumbelina befriends.
- Pat Musick as Mrs. Rabbit
- Neil Ross as Mr. Fox/Mr. Bear
- Tony Jay as Cow
- "Follow Your Heart (Intro)" - Jacquimo
- "Thumbelina" - Thumbelina, Farm Animals
- "Soon" - Thumbelina
- "Let Me Be Your Wings" - Prince Cornelius, Thumbelina
- "On the Road" - Mrs. Toad, Thumbelina, Singers de Espana (Los Sapos Guapos)
- "Follow Your Heart" - Jacquimo, Jitterbugs, Birds
- "Yer Beautiful, Baby" - Berkeley Beetle, Beetle Chorus
- "Soon (Reprise)" - Mother
- "Let Me Be Your Wings (Sun Reprise)" - Thumbelina
- "Marry the Mole" - Ms. Fieldmouse
- "Let Me Be Your Wings (Wedding Reprise)" - Cornelius
- "Let Me Be Your Wings (Reprise)" - Thumbelina, Jacquimo, Prince Cornelius
- "Follow Your Heart (Reprise)" - Chorus
- "Let Me Be Your Wings (Final)" - Barry Manilow, Debra Byrd
- This is the second time in which Jodi Benson, Kenneth Mars and Will Ryan appeared in a film adaption of a fairy tale by Hans Christian Anderson, the first being in The Little Mermaid, in which these respective actors voiced Ariel, King Triton, and the seahorse, respectively.
- This is, by far, the first animated film to be nominated for a Golden Raspberry Award and the first animated film to win a Golden Raspberry Award for worst in film; it won it for the song "Marry the Mole" in the category "Worst Original Song."
- During its theatrical release, it was released with the Animaniacs short "I'm Mad", which was later integrated into the TV series.
- Despite the film being a financial failure it has developed a cult following, and is sometimes called one of Don Bluth's better 90 films.
- In his review of the film, Roger Ebert said that there was hardly anything to enjoy. He rated it 2 & 1/2 stars out of 4.
- This is the first Don Bluth film to be shot in widescreen using the aspect ratio 1.78:1, it is cropped to 1.85:1 on the first DVD from Warner Bros. and on the 20th Century Fox DVD release.
Differences from the Source Material
- Thumbelina was born in a tulip.
- The female toad had only one son.
- Fish cut the water lily and a butterfly helped Thumbelina to drift in the river until the beetle caught her.