Sometime in the 1900s off the coast of Africa, a father, his wife, and infant son escape a burning ship and arrive in the unexplored jungles of Africa, where they build themselves a treehouse in which to live ("Two Worlds"). Meanwhile, a gorilla couple named Kerchak and Kala lose their son to a leopard named Sabor. As they move to another nest area, Kala hears an infant crying and follows it back to the treehouse. She investigates the treehouse and discovers that it is ransacked and the parents of the baby dead. As she looks around the treehouse, she notices a trail of large, bloody cat-like pawprints marked across the floor. Frightened, she rears back and finds a recent photograph of the family together. Kala hears more infantile crying and finds the human baby in an overturned basket. Immediately reminded of her own lost child, Kala feels remorse for the baby boy. Suddenly Sabor appears out of nowhere, hungry for human flesh. After a short chase, Kala and the baby escape the treehouse and run into the jungle to rejoin the gorillas. Upon arriving, Kala's mate Kerchak, also the leader of the gorillas, does not like the baby because he is human. Kerchak orders Kala to abandon the child, but Kala protests. Kerchak sympathizes with Kala and allows her to keep the boy, but he makes it clear that the child is hers and not his. Kala names the child Tarzan and treats him as one of her own ("You'll Be in My Heart").
As time passes, Tarzan, now ten years old, tries to fit in with the other gorillas ("Son of Man"). He makes friends with a female gorilla named Terk and an elephant named Tantor. 8 Years later, Tarzan grows up into an adult and is attacked by Sabor the leopard. Tarzan kills Sabor and earns the respect of Kerchak. Suddenly a gunshot is heard from far away. As the gorillas leave, Tarzan follows the sound and sees three humans: Professor Porter, his daughter Jane, and their hunter guide Clayton. Tarzan saves Jane from some angry baboons and tries to communicate with her as he can't speak English. Meanwhile, Terk, Tantor, and some of their gorilla friends stumble upon the campsite of the Professor, Jane, and Clayton. Mesmerized by the many strange human objects, the gorillas begin to destroy the entire camp ("Trashin' the Camp"). Jane and Tarzan return to the camp and find it ransacked by Tarzan's friends. After some introductions, Kerchak angrily appears. Tarzan and the gorillas leave and Prof. Porter and Clayton arrive.
Back in the jungle, Kerchak instructs the gorillas to stay away from the strangers. Tarzan protests, saying that the humans are not dangerous, but Kerchak is unwilling to believe him. Kala tries to make Tarzan understand the danger, but instead Tarzan angrily asks her why she never told him that there were others who look like him.
After some time, Tarzan secretly returns to the camp and is introduced to Prof. Porter and Clayton. Together, the three teach Tarzan about the human world ("Strangers Like Me"). Repeatedly Tarzan is asked about the whereabouts of the gorillas, but he is unwilling to disclose their location because of Kerchak. One day while returning to the campsite, Tarzan sees everything being packed up. He asks Jane what is happening, and she tells him that a boat has come to take the three back to England. Tarzan does not understand why Jane has to leave, but Clayton explains that if he leads them to the gorillas they would not have to leave. Tarzan leads them to Kala and Terk, but Kerchak appears and is hostile to Tarzan and his company. As the others flee, Kerchak scolds Tarzan and he angrily flees. Kala senses the sorrow in Tarzan and decides to show him the treehouse where she found him. There Tarzan finds the picture of his mother, father, and himself as a baby. Now knowing where he must go, Tarzan puts on his father's old formal suit and joins up with Jane, who has become infatuated with him. They board a ship only to find the crew captured by some thugs. Clayton reveals that he wanted to find the apes and capture them in order to sell them in England. He locks Tarzan, Jane, Porter and the crew into the hold and goes back to shore. Tantor and Terk rescue Tarzan and the others and they go off to stop Clayton.
The gorillas are attacked by Clayton and his gang and one by one they're rounded up. Kerchak is mortally wounded by Clayton's rifle but Tarzan interferes. As Jane, Porter, Tantor, and Terk free the gorillas and lock up the thugs, Tarzan and Clayton fight amongst the trees. Tarzan throws some vines at Clayton, entangling him. He starts cutting the vines with his machete and Tarzan sees one of the vines wrapping around Clayton's neck. He tries to warn the hunter but Clayton cuts the last vine and plummets to the floor, resulting in a death by hanging. A dying Kerchak apologizes to Tarzan for doubting him and makes him leader of the gorillas.
Tarzan says goodbye to Jane and Porter as they board the ship, but Jane decides that she loves him and returns, later followed by Porter.