Nine Allied powers signed Japan’s Instrument of Surrender in Tokyo Bay.
The signatories represented the United States, China, the United Kingdom, the Soviet Union, Australia, Canada, France, the Netherlands, and New Zealand. General Douglas MacArthur signed for the Allied powers as Supreme Commander, and each of those nine governments then had its own representative sign.
The number nine refers to Allied governments, not the total number of people who signed. Two Japanese representatives also signed, and MacArthur signed separately in his command capacity. Counting all individual signatures therefore produces a different total from counting Allied powers.
The participating countries reflected the coalition that had fought Japan across several theaters. China had been at war with Japan since 1937, while the Soviet Union entered the war against Japan in August 1945. Australia, Canada, France, the Netherlands, New Zealand, the United Kingdom, and the United States each contributed forces or territories to the wider Pacific and Asian conflict.