Three years later, in Butterfly’s house.

Suzuki is sitting before a figure of Buddha, praying to the Japanese gods. Butterfly remarks that those gods are lazy, for she is convinced that her husband’s god will answer prayers much more quickly. They have not seen Pinkerton in three years. They are nearly out of money. Suzuki warns that if Butterfly’s husband does not return soon, they will be ruined. Butterfly is adamant that he will return, in spite of Suzuki’s belief that foreign husbands never do. She recalls that on their last morning together, he told her that he would return when the robins make their nest. When Suzuki begins to weep, Butterfly comforts her and says that one lovely day they will see his ship in the harbour, and he will come to her (“Un bel dì”).

Sharpless arrives, and Butterfly welcomes him to her “American” house. He tries to show her a letter, but she is so delighted over the consul’s visit that she continually interrupts him to offer a tobacco pipe or American cigarettes. He tells Butterfly that Pinkerton has written a letter announcing his marriage to an American woman, but she prattles on and asks him when the robins will build their nests. Goro is heard laughing outside. She tells Sharpless that Goro is a bad man, for as soon as Pinkerton left, he besieged her with marriage offers from other men, including one from the rich Prince Yamadori. But Butterfly has rejected them all, despite her extreme poverty and isolation from her family.

Yamadori arrives (accompanied by strains of the Japanese national anthem) to repeat his proposal, but Butterfly firmly states that she is already married. When Goro points out that Pinkerton’s abandonment is equivalent to a divorce under Japanese law, she firmly states that her law is that of the United States, where, she believes, a judge would throw an erring husband into prison. She then goes to help Suzuki with the tea. Sharpless tells Goro and Yamadori that Pinkerton, who will soon arrive in Japan, does not want to see Butterfly. Sharpless has come to make sure she understands. Yamadori leaves with a heavy heart when Butterfly repeats her refusal.

Sharpless begins to read the letter, with joyful interruptions from Butterfly (“Letter Duet”). Pinkerton writes that perhaps Butterfly has forgotten him—she is astounded that he might think that—and that he is relying on Sharpless “to prepare her.” At this, Butterfly jumps up and cries out with excitement that finally he is returning to her. Sharpless gives up, cursing Pinkerton, and asks Butterfly what she would do if Pinkerton never came back. Shocked, she replies that she could do one of two things: either go back to being a geisha or, better, die.

Embarrassed for her, Sharpless begs her to accept Yamadori’s proposal, but Butterfly is stunned and hurt and asks him to leave. Then, crying, “Has he forgotten me?” she runs out of the room and returns with her child, a blond, blue-eyed, curly-haired little boy. Pinkerton does not know about the child, for he left before her pregnancy was evident. She urges Sharpless to write to Pinkerton with the news. Then she imagines having to beg and sing in the streets to earn their living, and she swears that she would rather die. She tells Sharpless that today the child’s name is Trouble, but when his father returns, he will be called Joy. Sharpless takes his leave, promising to write to Pinkerton. Moments later, Suzuki rushes in, dragging Goro and cursing him, for he has been spreading the lie that no one knows the identity of Trouble’s father. Butterfly pulls out her father’s knife, shouts that Goro is a liar, and threatens to kill him; then she throws him out.

As she reassures the child that Pinkerton will take them far away, a cannon shot is heard. Butterfly and Suzuki rush to the door to look at the harbour; it is Pinkerton’s ship, the Abraham Lincoln. Butterfly’s love is vindicated. They fill the room with flowers (“Flower Duet”). Butterfly dresses in her wedding clothes and, with Suzuki and Trouble, sits by the door and waits, watching the harbour, throughout the night. (The “Humming Chorus” is heard in the distance.)