In 1898, he became involved in administering institutes and became: He established Guangfuhui in 1904 and joined Tongmenghui in Paris the next year, and became a member of the Chinese anarchist group led by Wu Zhihui, and Li Shizeng.

He studied philosophy, psychology, and art history in the Universität Leipzig of Germany in 1907 under Karl Lamprecht and Wilhelm Wundt.

There he resumed his support, begun in his Paris years with Li Shizeng, for the Diligent Work-Frugal Study Movement, which sent worker-students to France.

He and a wide circle of colleagues founded the China League for Civil Rights which criticized the national government and Chiang Kai-shek for abuse of power.

The situation worsened, however; the League could not attain the release from jail of Chen Duxiu, Cai's former dean at Peking University, for instance.

After a period of shock and reflection, Cai retired from public view in a statement denouncing the political repression of the Nanjing government.

[8] After the outbreak of the Second Sino-Japanese War in 1937, partly because of declining health, instead of accompanying the national government to Sichuan, Cai moved to Hong Kong.

[5] Cai raised the traditional virtue of “righteousness (义), reciprocity (恕) and humanity (仁)” based on the Western ideas of "Freedom, equity, fraternity".

[5] Among the teaching staff at Peking University, there were many representatives of the new cultural movement such as Li Dazhao, Hu Shih, and Chen Duxiu.

He also assembled notable conservative and old-fashioned scholars such as Gu Hongming and Liu Shipei to teaching at Peking University.

[11] He believed in the subordinate, Confucian, relationship between husband and wife, holding that men rule outside the house, and women inside it (男主外女主内).

[14] Cai Yuanpei proposed that the formation of a new civil religion can be achieved by cultivating the Chinese to learn aesthetics, democracy, and science.

[12] Les Jean Jacques Rousseau en Chine : Cai Yuan Pei et John Dewey (French Edition): 9781493536009: de Shazer, Marie-Laure