ACT I

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 procured for him a geisha wife known as Madama Butterfly (Cio-Cio-San). To the American Consul, Sharpless, who arrives breathless from climbing the hill, Pinkerton describes his carefree philosophy of a sailor roaming the world in search of pleasure. For the moment, he is enchanted with the fragile Cio-Cio-San and intends to undergo a marriage ceremony with her – a 999-year contract, but subject to monthly renewal. When Sharpless warns that the girl may not take her vows so lightly, the lieutenant brushes aside such scruples, adding that he will one day take a 'real' American wife.

Cio-Cio-San is heard in the distance joyously singing of her wedding day. After she has entered, surrounded by her friends, she tells Pinkerton how, when her family fell on hard times, she had to earn her living as a geisha. Soon her relatives arrive and noisily express their opinions of the marriage. In a quiet moment, Cio-Cio-San shows the bridegroom her little store of possessions, one of which she hides from public view. Goro explains that it is a sheathed knife which the Mikado sent to Butterfly's father, with the 'invitation' to commit hara-kiri – which he obeyed. Butterfly confesses to Pinkerton that she, on the previous evening, secretly went to the Mission and adopted the religion of her new husband.

The wedding ceremony completed, the guests toast the couple. Suddenly Cio-Cio-San's uncle, a priest, bursts upon the scene, cursing the girl for having renounced her ancestors' religion. Pinkerton angrily orders priest and family to leave.

Alone with his bride, he dries her tears in the moonlit garden, where they discover the depths of their love.