As recorded in a China Mail (a Chinese newspaper) on 4 June 1923, there was controversy in relation to a case involving 50,000 yuan and Sun Fo.

[citation needed] In 1931, the near civil war caused by the arrest of Hu Hanmin and the invasion of Manchuria forced Chiang Kai-shek to resign.

During this time, he gained the reputation of having an "iron neck" —an outspoken liberal against Chiang Kai-shek's authoritarian tendencies, he could not be purged because he was the son of Sun Yat-sen.

Leading the left wing of the Kuomintang, he advocated cooperation with the CCP in the fight against the Japanese military occupation of 1931–1945, and represented his party in negotiations with Zhou Enlai.

[citation needed] Following the full-scale Japanese invasion of 1937, Sun Fo was tasked with obtaining military assistance from the Allied Powers.

But while Chiang Kai-shek wanted the arms primarily to fight the CCP, Sun Fo insisted that the threat to China's national integrity came foremost from the invading outside forces.

[citation needed] At the end of the Chinese Civil War in 1949, he exiled himself to Hong Kong until 1951, and moved to Europe (stops in Paris and Spain) from 1951 to 1952, and finally resided in the United States (Los Angeles) from 1952 to 1965.