This article is an assessment of the bosei hogo ronsō (the controversy over the protection of motherhood) which developed between 1916 and 1919 among four female protagonists—Hiratsuka Raichō, Yosano Akiko, Yamakawa Kikue and Yamada Waka. It describes the origin and development of the controversy in the light of international and domestic social and political changes affecting women in Japan in the 1910s. It examines each protagonist's views on the rights and wrongs of the state protecting motherhood, and compares their positions. It also discusses the influence which Western feminists such as Olive Schreiner and Ellen Key had on the debate, and the conclusion which the debate reached. The article finally reviews the achievements and limitations of this key debate, and assesses the impact the controversy had on the Japanese women's movement.