On a terrace above Nagasaki harbour, US Navy Lieutenant B F Pinkerton inspects the house he has leased from a marriage broker, Goro, who has also procured for him a geisha wife. To the American Consul, Sharpless, Pinkerton describes his carefree philosophy of a sailor roaming the world. When Sharpless warns that the girl may not take her vows so lightly, Pinkerton brushes aside such scruples.
Cio-Cio-San is heard in the distance. Surrounded by her friends, she tells Pinkerton how her family fell on hard times and how she had to earn her living as a geisha. In a quiet moment, she shows him a sheathed knife that the Mikado sent to her father, with the ‘invitation’ to commit hara-kiri – which he obeyed. Butterfly confesses that she has secretly been to the Mission and adopted the religion of her new husband.
Suddenly Cio-Cio-San’s uncle, a priest, bursts upon the scene, cursing the girl for having renounced her ancestors’ religion. Pinkerton angrily orders them all to leave.
Alone with his bride they discover the depths of their love.
Years later, Cio-Cio-San still waits for her husband’s return. Her maid, Suzuki, reveals how little money is left but is told to have faith: one fine day Pinkerton’s ship will appear on the horizon. Meanwhile, Sharpless arrives with a letter from Pinkerton asking him tactfully to inform Butterfly of his marriage with an American woman, but his attempts are frustrated by her constant questions.
Goro brings in a suitor for her hand, the wealthy Prince Yamadori, but Cio-Cio-San dismisses him, insisting that her American husband has not deserted her. When Sharpless suggests that Pinkerton may never return, she proudly shows him her child, insisting that as soon as Pinkerton knows of his son he will surely come back.
A cannon shot signals the arrival of Pinkerton’s ship in the harbour below. Cio-Cio-San and Suzuki strew the house with flower petals and begin their night’s vigil.
As dawn breaks, Pinkerton and Sharpless arrive with Pinkerton’s wife, Kate, remaining discreetly outside. They have come to enlist Suzuki’s support in persuading Butterfly to let them adopt the child. Pinkerton, overcome with remorse, rushes away.
Butterfly runs in but is taken aback when she sees only Sharpless and a foreign lady. She guesses the truth and agrees to give up her child if Pinkerton will return for him. Taking the dagger with which her father committed suicide, she bids farewell to her child, stabs herself and dies.