This study explores the socioeconomic selectivity of Japanese male immigrants who migrated to the continental United States (US) during the Age of Mass Migration (mid-nineteenth to the early twentieth century) by comparing the US administrative records of Japanese long-term immigrants interned during World War 2 (WRA records) with a Japanese social survey of non-migrants (SSM survey). Both data contained information on educational attainment in Japan, the father's occupation in Japan, birth cohort, and birth prefecture. The analysis revealed positive educational selectivity of the long-term migration of both secondary- and tertiary school-educated Japanese males in all the migratory time periods. The selectivity of secondary school-educated Japanese males was especially strong and extended to males from all family backgrounds and all Japanese prefectures. Given the strong middle-class nature of secondary and tertiary education in the late nineteenth to early twentieth century in Japan, the results showed that first-generation Japanese immigrants were positively selected in terms of their socioeconomic status. These findings are important because the growing literature on socioeconomic selection in migration during the Age of Mass Migration has predominantly focused on transatlantic (Europe-US) migration and has largely neglected transpacific migration from Asia.