This study explores how mothers of children who are young adults with developmental disabilities in South Korea experience identity strain and tension when they engage in advocacy on behalf of their children. Based on in‐depth interviews with 20 mothers in Korea who are members of parents’ advocacy groups, this article found that women experienced feelings of tension that arose when they deviated from normative understandings of what it means to be “devoted mothers.” Furthermore, they created two alternative versions of maternal roles—professional “I” mothers and professional “WE” mothers—that supported their identities as “disability advocates” in order to alleviate their emotional experiences. Such differences led them to practice different styles of advocacy in their interactions with disability welfare services. Based on these findings, this article discusses identity strain that emerges during the mothers’ political engagement on behalf of their disabled children. In doing so, it contributes to expanding current attention to parental advocacy activities in order to more deeply understand women's agential power to force social change and to act against existing state policies and power.