Following the death of Mao in 1976, agrarian decision-making shifted from the collective to individual households, unleashing rapid growth in farm output and unprecedented reductions in poverty. In new data on reform timing in 914 counties, we find an immediate trend break in the fraction of male children following rural land reform. Among second births that followed a firstborn girl, sex ratios increased from 1.1 to 1.3 boys per girl in the four years following reform. Larger increases are found among families with more education and in counties with larger output gains due to reform. Proximately, increased sex selection was achieved in part through prenatal ultrasounds obtained in provincial capitals. The land reform estimate is robust to controlling for the county-level rollout of the One Child Policy. Overall, we estimate land reform accounted for roughly half of the increase in sex ratios in rural China from 1978-86, or about 1 million missing girls.