What was the title of the written document that formally ended Japan’s participation in World War II?

The written document that formally ended Japan’s participation in World War II was the Japanese Instrument of Surrender.

Representatives of Japan and the Allied nations signed the instrument aboard USS Missouri in Tokyo Bay on September 2, 1945. It set out Japan’s acceptance of the terms of the Potsdam Declaration and formalized its capitulation.

The document was signed first by Mamoru Shigemitsu for the Japanese government and Yoshijirō Umezu for Imperial General Headquarters. Douglas MacArthur then signed for the Allied Powers, followed by representatives of nine Allied nations.

The Instrument of Surrender is not the same as the Potsdam Declaration, which was an Allied statement of surrender terms issued in July 1945. Nor is it the Treaty of San Francisco, which was a later peace treaty signed in 1951.