We study the effects of immigration restrictions on the intergenerational mobility of US-born men in the United States. We link US-born sons observed in 1900, 1920, and 1940 full-count Censuses to their fathers, and construct a measure of county-level exposure to the 1920s immigration acts, which sharply curtailed immigration from Southern and Eastern Europe. Exploiting this policy-induced variation, we find that the quotas reduced intergenerational mobility among US-born white men, but had no adverse effect for Black men. Among whites, losses were smaller for sons of richer fathers, who were more likely to migrate away from highly exposed areas. Evidence from the 1940 Census indicates that exposed white men were less likely to be employed and earned lower wages in adulthood, consistent with both occupational downgrading and reduced productivity within occupations. We show that these effects operated through both reduced immigrant–native complementarities and incomplete substitution from unrestricted migration, while human capital investment can explain at most only a modest part of the total effect.