This study recognizes family management of large Korean business groups (chaebols) as an institution existing within the Korean economic system, and analyzes the interests and ownership structures upon which it operates and is maintained. Through empirical analysis of the determinants of family ownership stakes using 1,061 firm-year observations from 11 business groups that were continuously designated as equity investment ceiling groups from 2001 to 2006, this study found that the owner-manager families of business groups, instead of pursuing economic interests based on individual firm performance as investors, make equity investment decisions that consider factors related to control over the entire group and social legitimacy. In particular, families actively utilize relational resources arising from cross-shareholding relationships among affiliates in the process of maintaining control over the entire group, suggesting that the efficiency-centered perspective that views business groups simply as the sum of individual firms has certain limitations. By examining the motivations and interest factors upon which owner-manager families—who experienced a critical institutional transition triggered by the Asian financial crisis—base their decisions to increase direct investment levels in affiliates in Korea, where business groups are the dominant organizational form, this study can broaden the perspective for understanding governance issues of large Korean business groups.