Originally titled Bears, it 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 the fellow Disney/Pixar film Finding Nemo. A 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), Denahi (voiced by Jason Raize) and Sitka (voiced by D.B. Sweeney), return to their tribe in order for Kenai to receive his sacred totem, its meaning being 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, much to his objections, stating that bears are thieving monsters. He believes his point is made a fact when a bear steals some salmon. Kenai and his brothers follow the bear's trail; when they find the bear, Kenai recklessly throws rocks at it. Provoked, the bear attacks Kenai and he and his brothers battle the animal on a giant glacier. When the bear gets the upper hand, Sitka sacrifices himself to save his brothers by causing both himself and the bear to fall off the glacier. However, the bear survives and runs into the woods.
After Sitka's funeral, Kenai, outraged that Sitka died and the bear was allowed to live, heads out to avenge his elder brother. He chases the bear up onto a mountain and engages it in a fight, eventually stabbing it and killing it. The Spirits, represented by Sitka's spirit in the form of a bald eagle transforms Kenai into a bear after the dead bear's body disappears. Denahi arrives, and, mistaking Kenai for dead and his bear form is responsible for it, vows to avenge Kenai.
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 to find Sitka and be turned back to normal, but only when he corrects what he had done wrong; she quickly disappears without an explanation. Kenai quickly discovers the wildlife can talk, meeting two brother mooses, Rutt and Tuke (voiced by Rick Moranis and Dave Thomas). 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 fails multiple times to kill Kenai, still unaware that he is his brother. 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. Next, the bears encounter some cave paintings, a pair of rams arguing with their own echo, and a land of geysers. 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 the late Michael Clarke Duncan), a huge Grizzly Bear. Kenai becomes very much at home and at content with the other bears. During a discussion among the bears, Koda tells a story about his mother fighting human hunters on a glacier, 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 heartbroken, because he is an orphan now. Unable to apologize to Koda because he can't find the cub, Kenai leaves to climb the mountain himself. Rutt and Tuke, having fallen off the mammoths (Rutt having lost an antler in the process), reform their brotherhood in front of Koda, prompting him to go after Kenai. Denahi confronts Kenai on the mountain, but their fight is intervened by Koda who steals Denahi's hunting spear. 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. Even though he can't talk to humans, Koda doesn't want Kenai to leave, because ever since he came into the cub's life, he has been like a brother to him. 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 paints his paw print on the village wall. At last, Kenai gains his title as a man, through being a bear.