Kenai (voice of JOAQUIN PHOENIX), Denahi (voice of JASON RAIZE) and Sitka (voice of D.B. SWEENEY) are brothers growing up in prehistoric times when mammoths still roam the land. Kenai, the youngest, is set to receive his totem, a symbol that will lead him into manhood and throughout the rest of his life.
Accordingly, he's disappointed when the village shaman, Tanana (voice of JOAN COPELAND), presents him with the totem of Love. He doesn't have much time to think about it, however, as he discovers that a bear has taken the basket of fish he was supposed to have secured. He goes off to retrieve it, but finds more trouble than he expected as he encounters a large and ferocious bear. Denahi and Sitka arrive to help, with Sitka eventually sacrificing his life to save those of his brothers.
Filled with hatred and a lusting for revenge, Kenai again sets out to find the bear, with Denahi not far behind. Kenai ends up killing the bear, but Sitka's spirit decides it's time for his younger brother to grow up and learn a lesson. Thus, he causes Kenai to transform into a bear, a development that obviously doesn't sit well with the bear hater and that Denahi doesn't see, thus leading him to believe that this new bear killed Kenai.
Tanana tells the new bear that he must take up the matter with his brother at the place where the light touches the earth. He then sets out on his journey where he encounters two wacky moose, Rutt (voice of RICK MORANIS) and Tuke (voice of DAVE THOMAS), who prove to be of no help. After getting caught in a bear trap, he meets the young and talkative bear cub, Koda (voice of JEREMY SUAREZ), who agrees to help him escape if he'll take him to the annual Salmon run.
Kenai initially wants nothing to do with Koda, but when he hears that the bear gathering, led by Tug (voice of MICHAEL CLARKE DUNCAN), is near that place where the light touches the earth, he agrees. Along the way, Kenai learns various lessons about himself and others, all while the two must deal with Denahi who's intent on revenging his two brothers' deaths.