This film tells the story of a sixteen year old mermaid Ariel who is dissatisfied greatly with her life under the sea. Paying no attention to the warnings of her father, King Triton, and the court musician, the crab Sebastian, Ariel and her best friend, Flounder the fish frequently reach the surface of the ocean, and with the help of the goofy seagull named Scuttle, they collect human artifacts.

Regardless of her awareness of the forbidden contact between humans and sea people, Ariel strives to become part of the human world. Hiding in her secret cave, Ursula, who has been looking for a chance to take revenge on King Triton for bashing her from the kingdom decides to take advantage of this wonderful opportunity.

That night when Ariel and Flounder sneak up to the surface of the ocean, they view a fireworks display in celebration of the birthday of Prince Eric. When a storm destroys his ship, Prince Eric almost drowns in the ocean before Ariel saves him and starts to like him.

After King Triton discovers that his daughter has fallen in love with a human, he destroys all of her treasures that are connected with the human world. Unseen by anyone, Ursula brings Ariel to her underwater cave and makes a deal with the fairy princess to transform her into a human for three days in which she must give the kiss of true love to the prince; otherwise she will be turned into a mermaid on the third day. In case Ariel fails to remain a human, she will be turned into a polyp. As payment, the witch takes Ariel's voice making her unable to speak.