ABSTRACTThis study provides new evidence on on the causal effect of fertility on maternal labor supply in rural China, using the fact that in some parts of rural China couples are allowed to have a second child if their firstborn is female. Estimates show that a second child reduces maternal labor force participation by 4.6 percentage points, labor supply intensity (hours worked conditional on employment) by 1.4 h per week and monthly income by 54.5 Chinese Yuan (18.7 percent). Further, the labor supply of mothers whose husbands are rural-to-urban migrants is the most sensitive to having an additional child, likely because they have more difficulty balancing farming and childcare. Conversely, labor supply is not reduced by fertility for mothers living in three-generation families, most likely because grandparents can provide both time and money to help with childcare.