A young American Navy Lieutenant, Benjamin Franklin Pinkerton, is inspecting a home overlooking Nagasaki Harbor which he has rented from Goro, the marriage broker, who also has arranged for Pinkerton's marriage to Cio-Cio-San (Butterfly), a 15-year old geisha. He is joined by Sharpless, the American Consul, who chides him for his casual attitude toward the marriage. Sharpless warns Pinkerton that his bride may not take her vows so lightly, but Pinkerton is unmoved and proposes a toast to the American woman that he will marry one day. Butterfly appears and introduces her friends and relatives. The marriage ceremony is then performed by the Imperial Commissioner. The celebration is rudely interrupted by the Bonze, a Japanese priest, who bitterly denounces Butterfly for having forsaken the faith of her fathers. Pinkerton orders everyone to leave and tries to console his bride. As twilight approaches Butterfly's maid, Suzuki, helps her change from her wedding dress, and the newlyweds are left alone to sing a passionate love duet before retiring to the house.
It is three years later and Pinkerton has long since left Japan. Butterfly has borne him a son, named Trouble, but is virtually penniless. Suzuki implores the gods for help, but Butterfly is sure that Pinkerton will return as promised, when the robins again nest in the spring. She describes the joy that will be hers when Pinkerton ' s ship enters the harbor. Sharpless arrives with a letter announcing Pinkerton ' s return with his American wife, but before he can read it to Butterfly, Goro enters with Prince Yamadori, a wealthy nobleman who wishes to marry Butterfly. She reminds him she is already married and they leave. Sharpless finally reads Pinkerton ' s letter to a disbelieving Butterfly, who brings in her son and tells Sharpless she is convinced that when Pinkerton learns of their child he will return to her. Deeply moved, Sharpless leaves, promising to tell Pinkerton of his son. Suzuki enters berating the whimpering Goro, who has been telling people the baby ' s father is unknown. Butterfly threatens to kill Goro, but Suzuki saves him. Cannon in the harbor announces the arrival of a ship. With a telescope, Butterfly identifies it as Pinkerton ' s ship Abraham Lincoln . Butterfly puts on her wedding gown while Suzuki dresses the child, and they take up their vigil, watching for Pinkerton ' s return. Eventually, Suzuki and Trouble fall asleep, but Butterfly waits patiently as a sad humming is heard in the background.
At dawn, Suzuki sends Butterfly and her son to rest. Pinkerton, his wife Kate and Sharpless enter. Sharpless explains to Suzuki that Kate and Pinkerton have come to take the child. Suzuki breaks down in despair, and Pinkerton leaves after singing a heartbroken farewell. Suzuki agrees to tell Butterfly, after being assured by Kate that she will treat the child as her own. Butterfly enters eagerly looking for Pinkerton, but upon seeing Kate, she realizes they will take her child from her. She agrees to give up her son, but only if Pinkerton will return for him in person. Butterfly sends Suzuki to the garden, and then stabs herself with an ancestral dagger which is inscribed: Death with honor when one can no longer live in honor . She dies as Pinkerton rushes in sobbing her name.