The main objective of this study aims to discern the relation between child-rearing involvement and intergenerational co-rearing for grandmothers and mothers in dual-earner families, in turn to explore the differences in child-rearing involvement and intergenerational co-rearing for grandmothers and mothers. The relations among background information, child-rearing involvement of the grandmother and mother, and intergenerational co-rearing were also explored. The study used the questionnaire interview method by focusing on grandmothers assisting in co-rearing grandchildren in dual-earner families who at least had one young child aged 2 to 6 alongside whose daughter-in-law. The study adopted the “Child-rearing involvement for grandmothers and mothers” measurement and the “Intergenerational co-rearing for grandmothers and mothers” measurement as the study tools. With interview subjects focusing on grandmothers, who may had difficulties reading the questionnaire, the study had adopted the one-on-one interview method, with which to conduct the interview, and collected a total of 377 valid questionnaires. The study data were analyzed by using statistical methods, including the descriptive statistics, t-test, ANOVA, and correlation analyses. The key findings were as followed, The grandmother’s child-rearing involvement and the mother’s child-rearing involvement tended to manifest in the form of offering warmth and encouragement, but less in providing diverse experience and stimulants. The grandmother reported that the mother’s child-rearing involvement was found to exceed the grandmother’s child-rearing involvement, which revealed that the child’s mother in a dual-earner family remained the primary child caregiver. Grandmother’s and mother’s education had significant association with supportive behaviors of intergenerational co-rearing for grandmothers and mothers. Mother’s age had significant association with supportive and unsupportive behaviors of intergenerational co-rearing for grandmothers and mothers. The correlation analyses indicated that the more grandmothers perceived grandmother’s child-rearing involvement and mothers’ child-rearing involvement, the more grandmothers and mothers had supportive behaviors of intergenerational co-rearing, and the less unsupportive behaviors of intergenerational co-rearing, and vice versa . At last, the study proposed recommendations, based on the study findings, offering reference pointing to the family educators in intergenerational co-rearing for grandmothers and mothers in developing family education, and a feasible direction to future researchers.