Nine Allied countries signed Japan’s Instrument of Surrender after the Japanese delegation signed in 1945.
General Douglas MacArthur signed first for the Allied powers, followed by Fleet Admiral Chester Nimitz for the United States. Representatives then signed for China, the United Kingdom, the Soviet Union, Australia, Canada, France, the Netherlands, and New Zealand. Counting those national representatives gives nine Allied countries.
The ceremony took place aboard USS Missouri in Tokyo Bay on September 2, 1945. The document was signed by Japanese representatives before the Allied representatives added their signatures. The sequence reflected both the formal surrender and the broad coalition that had fought Japan.
A common counting error is to include MacArthur as a national representative or to count only the major powers. MacArthur signed as Supreme Commander for the Allied Powers, while Nimitz and the other representatives signed for individual governments. The nine-country total refers to the national signatories after Japan.