On the square in front of the imperial palace, a mandarin informs the crowd about the imminent execution of the Prince of Persia. The young man aspired to marry Princess Turandot but has failed to answer her riddles. In the crowd there are the Prince, who conceals his identity, and his father Timur, the exiled Tatar tsar. The moon is rising and the Prince of Persia is on his way to be executed.
Turandot appears. The Prince is entranced by her beauty and decides to solve the riddles. The imperial ministers Ping, Pong and Pang try to dissuade him. Timur and his slave Liu, who is secretly in love with the Prince, beg him to leave Beijing with them. The Prince is ready for the challenge and strikes the gong.
Ping, Pong and Pang prepare themselves for either the Prince's wedding or his funeral. They complain about the misfortunes that befell China with the birth of Turandot. People gather in the square again. Before the test begins, the Princess tells why she takes revenge on all men. Her grandmother Lo-u Ling was dishonored by a soldier. Turandot asks three riddles, and the Prince solves them. Turandot tells his father, Emperor Altoum, that she will die of shame if she marries. The Prince promises to forfeit his life if before morning Turandot can discover his name.
Heralds call out Turandot’s command: under penalty of death people must learn the name of the Prince overnight. The ministers are trying to find out his name from the Prince himself using temptations and threats. The guards drag in Timur and Liu, they may know the truth. Liu says that she alone knows the Prince’s name but will keep it as her secret out of love for him. She stabs herself. Timur takes her body and leaves Beijing.
Turandot is adamant. She does not want to repeat the fate of Lo-u Ling. The sun is rising. The Prince kisses Turandot and reveals his true identity — Calaf. Together they go out to the people. The Princess declares that the stranger's name is Love.