This research was studied 100 families who have mentally retarded adults at the social welfare centers or sheltered workshop in Seoul and Kyongggi-do to explore the relationship of family stress, family strain, family hardiness, and family adaptation by using the Resiliency Model of family Stress, Adjustment, Adaptation. Results from regression analysis revealed that family hardiness operated as a mediating factor between family stress and family adaptation. It was found through this study that the most influential factors affecting family adaptation are family hardiness, and marital period, and family strain and family stress have some effects on family adaptation not directly but indirectly. Findings provided evidence for the theoretical and empirical significance of family hardiness as a predictor of family adaptation. Further, these findings suggest that family hardiness is a influencing factor that is the resiliency of family who have a adults with mental retardation. Therefore, implications for practice such as a development of the program and policies for the families who have a adult with mental retardation are discussed in relation to the family hardiness of those families.