The film was the third and final Disney animated feature produced primarily by the Feature Animation studio at Disney-MGM Studios in Orlando, Florida; the studio was shut down in March 2004, not long after the release of this film in favor of computer animated features. The film received an Academy Award nomination for Best Animated Feature, but lost to another Walt Disney Pictures release, Pixar's Finding Nemo. A direct-to-video sequel, Brother Bear 2, was released on August 29, 2006.
The film is set in a post-ice age North America, where the local tribesmen believe all creatures are created through the Spirits, who are said to appear in the form of an aurora. Three brothers: Kenai (voiced by Joaquin Phoenix)- the youngest brother, Denahi (voiced by Jason Raize)- the middle brother -and Sitka (voiced by D.B. Sweeney)- the eldest brother, return to their tribe in order for Kenai to receive his sacred totem, a necklace in the shape of an animal. The particular animal it represents symbolizes what he must achieve to call himself a man. Unlike Sitka, who gained the eagle of guidance, and Denahi, who gained the wolf of wisdom, Kenai receives the bear of love, to which he objects, stating that bears are thieves. He believes his point is made a fact when a bear takes some salmon. Kenai and his brothers pursue the bear, but a fight follows on a glacier, during which Sitka gives his life to save his brothers, although the bear survives. Vengeful, Kenai heads out to avenge Sitka. He chases the bear up onto a mountain and kills it. The Spirits, represented by Sitka's spirit in the form of a bald eagle, transform Kenai into a bear after the dead bear's body disappears. Denahi arrives, mistaking Kenai as dead, and believing the bear is responsible, vows to avenge Kenai by hunting it down.
Kenai falls down some river rapids, survives, and is healed by Tanana (voiced by Joan Copeland), the shaman of Kenai's tribe. She does not speak the bear language, but advises him to return to the mountain -"where the lights touch the Earth"- to find Sitka and be turned back to normal, but only when he corrects what he had done; she disappears without an explanation. Kenai quickly discovers the wildlife can talk, meeting two brother moose, Rutt and Tuke (voiced by Rick Moranis and Dave Thomas, in a send-up of their famous characters Bob and Doug McKenzie). He gets caught in a trap, but is freed by a chatty bear cub named Koda (voiced by Jeremy Suarez). The two bears make a deal: Kenai will go with Koda to a nearby salmon run and then the cub will lead Kenai to the mountain. As the two eventually form a sibling-like bond, Koda reveals that his mother is missing. The two are hunted by Denahi who, still unaware that the bear he's pursuing is his brother, is determined to hunt down Kenai. Rutt and Tuke run into the bears multiple times, the group hitching a ride on a herd of mammoths to quicken the pace to the salmon run, but the moose are left behind when the bears move on. Kenai and Koda escape Denahi again and reach the salmon run, where a large number of bears live as a family, including the leader Tug (voiced by Michael Clarke Duncan), a grizzly bear. Kenai becomes very much at home and content with the other bears. During a discussion among the bears, Koda tells a story about his mother fighting human hunters, making Kenai realize that the bear he killed was Koda's mother.
Guilty and horrified, Kenai runs away, but Koda soon finds him. Kenai reveals the truth to Koda, who runs away, grief-stricken. An apologetic Kenai leaves to reach the mountain. Rutt and Tuke, having fallen out, reform their brotherhood in front of Koda, prompting him to go after Kenai. Denahi confronts Kenai on the mountain, but their fight is interrupted by Koda, who steals Denahi's hunting pike. Kenai goes to Koda's aid out of love, prompting Sitka to appear and turn him back into a human, much to Denahi and Koda's surprise. However, Kenai asks Sitka to transform him back into a bear so he can stay with Koda. Sitka complies, and Koda is reunited briefly with the spirit of his mother, before she and Sitka return to the Spirits. In the end, Kenai lives with the rest of the bears and gains his title as a man, through being a bear.
- Joaquin Phoenix as Kenai, the younger brother of Sitka and Denahi. After he needlessly kills a bear, Kenai is turned into one himself to teach him to see another's eyes, feel through another's heart, and discover the true meaning of brotherhood. John E. Hurst and Byron Howard served as the supervising animators for Kenai in human and bear form respectively.
- Jeremy Suarez as Koda, a wisecracking grizzly bear cub who helps Kenai on his journey to where the Lights Touch the Earth. Alex Kupershmidt served as the supervising animator for Koda.
- Rick Moranis as Rutt, a comic Canadian moose.
- Dave Thomas as Tuke, another comic Canadian moose.
- Jason Raize as Denahi, the middle brother. Ruben A. Aquino served as the supervising animator for Denahi.
- D.B. Sweeney as Sitka, the oldest brother.
- Joan Copeland as Tanana, the shaman-woman of Kenai's tribe.
- Michael Clarke Duncan as Tug, a wise old grizzly bear.
- Greg Proops as Male Lover Bear
- Pauley Perrette as Female Lover Bear
- Estelle Harris as Old Lady Bear
- Bumper Robinson as Chipmunks
- Angayuqaq Oscar Kawagley as Inuit Narrator
- Hope Levy as Valley Girl Bear
- Darko Cesar as Foreign Croatian Bear
- Frank Welker as Kenai (Roars) and Koda's Mother (Roars)
- Mickie McGowen as Koda's Mother a female grizzly bear