This paper examines the labor market performance of immigrants during the early twentieth-century America. In particular, we consider the immigrants from Europe, Asia, and South America who were present in America between 1900 and 1930 to investigate the degree of human capital transferability across the regions of origin. Accounting for the changes in unobserved immigrant quality across cohorts, we estimate the returns to work experience in the American labor market. The estimation results show that European immigrants assimilated into the American labor market fairly well while immigrants from Asia and South America did not, which is suggestive of imperfect human capital mobility. In addition, the estimation results obtained from synthetic cohorts indicate that the quality of immigrants was systematically different across years of arrival.