On receiving word of his appointment, Yoshizawa traveled from Europe back to Japan via the Trans-Siberian Railway and Manchuria to see conditions first-hand.

In the period immediately prior to the start of the Pacific War, Yoshizawa was appointed as a special envoy by Prime Minister Fumimaro Konoe to the Netherlands East Indies following the diplomatic mission of Ichizo Kobayashi.

Yoshizawa was assigned to present a new set of demands on the Dutch government in Batavia, which were deliberately intended to be unacceptable.

The negotiations dragged on unsuccessfully, and on 11 June 1941, the Liaison Meeting of the Imperial General Headquarters and Government decided to recall Yoshizawa and terminate the talks.

After the end of World War II, the surrender of Japan, Yoshizawa was purged from public office by the American occupation authorities.