This study aims to examine curvilinearly moderating effects of task interdependence on the relationship between demographic faultlines and group performance. It posits that the degree of task interdependence has an impact on the effects of demographic faultlines. It was conducted in six organizations in Korea, their industries including heavy industries, hospital, construction, petrochemical, fine chemicals, and system integration. The survey was distributed to 1330 individuals in 162 teams and 1082 individuals in 137 teams responded to the questionnaire. To test the hypotheses including nonlinear interactions, we conducted a hierarchical regression analysis to the survey data from 82 groups within six firms in Korea. The results show that for groups that experience a high level of task interdependence, the slope for the regression of demographic faultlines on group performance is comparatively low and, at the low level of task interdependence, insignificant. However, at intermediate levels of task interdependence, the association was strongly negative and significant. This study finds that the negative relationship between demographic faultlines and group performance is stronger when task interdependence is moderate than when task interdependence is high or low. Therefore, managers should pay attention to optimal group design by carefully assigning tasks in diverse and divided groups.