Lieutenant Pinkerton, an American naval officer, inspects a house overlooking Nagasaki harbor that he is leasing from Goro, a marriage broker. Pinkerton has just purchased this house in a deal which also includes a few servants and a young bride, Cio-Cio-san (Butterfly). The American consul Sharpless arrives. Pinkerton describes his philosophy of the fearless Yankee roaming the world in search of experience and pleasure. He is not sure whether his feelings for the young girl are love or a whim, but he intends to go through with the marriage ceremony. Sharpless warns him that the girl may view the marriage differently. Butterfly arrives with some of her friends. She tells that she comes from family which was once quite wealthy, but is wealthy no longer, so she had to become a geisha to try and support the family. The wedding is to take place at the house. Butterfly had been so excited to marry an American that she had earlier secretly converted to Christianity. During the wedding ceremony, her uncle, the Bonze, who has found out about her conversion, comes to the house, curses her and orders all the guests to leave, which they do while renouncing her. Butterfly remains alone with her husband who comforts her in his arms.
Three years have passed since the wedding. Pinkerton has left Nagasaki and only Suzuki, the maid, has remained with Butterfly. They live in poverty. Butterfly is still waiting for Pinkerton to return. Goro keeps trying to marry her off again, but she does not listen to him either. Sharpless comes to the house with a letter which he has received from Pinkerton. He attempts to read Pinkerton’s letter to Butterfly but she continually interrupts him, as
she misinterprets the content of the letter. When Sharpless asks what she would do if Pinkerton were never to return, Butterfly is deeply insulted. She reveals that she gave birth to Pinkerton’s son after he had left. The child’s name is «Sorrow», but when Pinkerton will return it will be «Joy». The harbor’s cannon is heard. From the hill house, Butterfly sees Pinkerton’s ship. She and Suzuki prepare for Pinkerton’s arrival, and then they wait.
Sharpless and Pinkerton arrive at the house, along with Pinkerton’s new American wife, Kate. She has agreed to raise the child. But, as Pinkerton sees how Butterfly has decorated the house for his return, he realizes he has made a huge mistake. He admits that he is a coward and cannot
face her, leaving Suzuki, Sharpless and Kate to break the news to Butterfly. Butterfly wakes up and searches desperately for her husband. But instead she sees Kate and immediately grasps the bitter truth. She agrees to deliver the child to Pinkerton if he himself will come to fetch him. Butterfly sends out Suzuki and the child, takes the dagger which her father used in order to kill himself and reads the inscription: «He dies with honor who cannot live with honor». She is interrupted momentarily when the child comes in, but Butterfly says goodbye and blindfolds him. She stabs herself as Pinkerton arrives, calling out for her.