China extended maternity leave to encourage childbirth following the suspension of the one-child policy. This study specifically investigates the effects of China's maternity leave reform (MLR) on women's labor supply, utilizing a difference-in-difference analysis with data from the China Family Panel Studies. Our findings show that MLR leads to a notable decrease in women's working hours, with an average reduction of 2.6 h per week. However, no corresponding impacts are observed in men's labor supply. Mechanism analysis suggests that these effects may stem from women facing more disadvantaged positions in the labor market, having increased intentions for fertility, experiencing heightened household responsibilities, and encountering reinforcement of traditional gender roles attitudes. These findings hold significant implications for the future design and implementation of childbirth promotion and gender equality policies.