This paper examines the economic mobility of foreign migrants in Japan. In a country that is largely regarded as homogeneous and closed to outsiders, how and to what extent do immigrants achieve economic success? A survey conducted by the authors revealed that the conventional assimilationist perspective does not fully explain immigrants’ economic success in Japan. Migrants from the West experience what Chiswick and Miller () refer to as “negative assimilation.” That is, their earnings decline over time in Japan. While negative assimilation was not clearly observed among immigrants from neighboring Asian countries, wages among them did not increase with the length of their stay in Japan. For both groups, the skills they brought from abroad were found to be largely accountable for their economic success, while locally specific human capital, such as education acquired in the host society, did not contribute to their earnings.