Nine Allied nations signed Japan's Instrument of Surrender at the 1945 ceremony.
The Allied signatories represented the United States, China, the United Kingdom, the Soviet Union, Australia, Canada, France, the Netherlands, and New Zealand. Douglas MacArthur signed first as Supreme Commander for the Allied Powers, followed by Fleet Admiral Chester Nimitz for the United States and the representatives of the other Allied governments.
The number nine refers to Allied nations, not the total number of people who signed. Two Japanese representatives also signed: Mamoru Shigemitsu for the Japanese government and Yoshijirō Umezu for Imperial General Headquarters.
The ceremony took place aboard USS Missouri on September 2, 1945. The document formalized Japan's surrender after the emperor's August 15 announcement, so the public announcement and the international signing ceremony occurred on different dates.