The present study, based on a sample of 1649 mothers in Korea, examines dimensions of maternal self-concept and their differences across a broad range of motherhood phases i.e., among mothers of preschoolers (ages 2–5), school-aged children (ages 6–12), and adolescents (ages 13–18). Overall, seven dimensions of maternal self-concept were identified across the three stages of motherhood. Among them only two dimensions, knowledge and skills in parenting and interpersonal relationships, were found in all three groups of mothers. The most notable differences lie in the self-as-individual dimensions (i.e., self-development, self-reflection, and independence); they were manifested among mothers of pre-schoolers or school-aged children, but not among mothers of adolescents. This study also documents differences in predictive relationships between maternal self-concept and mothers’ well-being according to the ages of their children. We conclude that maternal self-concept and its predictors are different at different stages of child development.