<p>Studies of subjective forms of immigrant integration, such as immigrants’ subjective well-being, are rare, but have grown in the past few decades for major immigrant destinations. This study extends the understanding of subjective well-being among immigrants by focusing on a non-traditional destination country, Japan, where the number of foreign residents has risen continuously in recent years. Specifically, the aim of this study is to examine whether and how the association between social capital and life satisfaction is moderated by the duration of residence among immigrants in Japan, using a nationally representative dataset, the 2018 Survey of Foreign Citizens Regarding Life and Work. In contrast to the expectations of assimilation theory, the results show that length of residence is negatively associated with life satisfaction, while social capital, both in terms of bonding social capital (social networks within the ethnic group) and bridging social capital (social networks across ethnic boundaries), is positively associated with life satisfaction. However, while bonding social capital is positively associated with life satisfaction among immigrants with shorter lengths of residence, this association is weaker among those with longer residence. Overall, the findings suggest that although some immigrants develop ties to Japanese society, life satisfaction is lower among immigrants with longer residence, and generally low levels of bridging social capital point to persistent barriers to integration.</p>