The purpose of this research is to validate the determinants of information systems(IS) sourcing strategy focusing on Korean financial institutions. Based on the factor analyses and discriminant analyses using data from 34 major Korean financial institutions, we observed that determinants of IS souring strategy are perceived risks, strategic expectations and organizational IS maturity. If the clients have clear objectives, can control the risks from IS sourcing, and have information systems in the less-matured stage, they frequently outsource their IS. In view of the IS maturity, previous studies suggest that more-matured IS are outsourced. But the results of this study show that more-matured IS are insourced. These phenomena can be explained by classifying IS by their functions. Transaction processing systems, which are mission-critical, are generally insourced, but decision support systems, which are in their mature state, are generally outsourced.