How did Protestant female missionaries influence women’s political participation in colonial Korea? Under Joseon Confucian norms, women were excluded from education and public life. The first Western female missionary arrived in 1885 and trained Korean “Bible women,” creating spaces for women’s education and organization during colonial rule (1910–1945). While existing research examines missionary effects on education and fertility, impacts on political participation remain unexplored. Using historical mission records and data on independence activists, I find that greater exposure to female missionaries led to greater female political activism. Gender-specific ordinary least squares analysis reveals that female missionary exposure strongly predicts women’s activism, whereas it has no effect on men. To strengthen causal identification, I employ missionary children as an instrumental variable. Mechanisms operate through female role models and informal networks, including Bible classes and home visits. These findings provide the first systematic evidence linking Protestant missions to women’s political empowerment before suffrage, with effects persisting in female political representation after 1945.