Introduction  The demographic composition of the ethnic Korean population in Japan (often referred to as zainichi) shows a declining birthrate. However, zainichi who live in zainichi Korean communities have more children than zainichi living in predominantly Japanese communities. Social capital (SC) can increase societal efficiency by promoting cooperative behavior within communities. This study clarified the family formation and SC that supports childcare for zainichi mothers living in zainichi Korean communities.Methods  We conducted semi-structured interviews with 10 zainichi mothers living in zainichi Korean communities in Japan. We qualitatively and descriptively analyzed the family formation and SC that support childcare in this population. The Ethical Committee of Osaka Prefecture University approved this study and the participants gave their written informed consent.Results  We extracted three categories and 12 subcategories for “thoughts on current family formation” and four categories and 11 subcategories for “SC supporting childcare.” Zainichi mothers living in Korean communities “think consciously about marriage” and “think positively about having multiple children and family formation,” but they have “concerns about childbearing and child-rearing.” “People who support childcare practically and mentally” and “childcare services” were also identified as important factors. Although zainichi mothers felt dissatisfied with “support that they wanted to use but found difficult to use,” they considered childcare support as human and physical SC. As an additional resource, they felt that “the zainichi community fosters security and bonding,” and thus promotes SC for child-rearing.Discussion  Networks with common norms, values, and understanding facilitated cooperation among zainichi mothers. “The zainichi community, which fosters security and bonding,” may support family formation through engendering a positive perception of child-rearing.