Saneatsu enrolled in the sociology department of Tokyo Imperial University, but left without graduating in 1907 to form a literary group with Kinoshita Rigen, Shiga Naoya, Arishima Takeo, and Ogimachi Kinkazu (ja:正親町公和).

Through the medium of Shirakaba, Mushanokōji began moving away from the Tolstoy ideal of self-sacrifice, and promoted his philosophy of humanism as an alternative to then-popular form of naturalism.

In 1918, Mushanokōji took the next step in the development of his philosophy by moving to the mountains of Kijō, Miyazaki in Kyūshū, and establishing a quasi-socialistic utopian commune, Atarashiki-mura (New Village) along vaguely Tolstoyan lines.

His idealism appears in his autobiographical novel Aru otoko (或る男, A Certain Man) (1923), and in the play Ningen banzai (人間万歳, Three Cheers for Mankind) (1922).

However, Mushanokōji tired of the social experiment and left the village in 1926; a dam project forced it to relocate to Saitama Prefecture in 1939, where it still exists.

After the Great Kantō earthquake of 1923, Mushanokōji returned to Tokyo to run an art gallery, and started to sell his own paintings, mostly still lifes depicting pumpkins and other vegetables.

Publication of Shirakaba was suspended after the earthquake, but Mushanokōji went on to bring out the literary magazine, Fuji, with the novelist and playwright Nagayo Yoshirō.