This study aimed to examine effects of Acceptance and Commitment Therapy(ACT) on parenting anxiety, psychological acceptance, and mindfulness of mothers of preschool and school-aged children. For this purpose, 26 mothers of the preschool and school-aged children in Seoul and Gyeonggi area were assigned to the two distinct groups. Thirteen of the mothers were assigned to the Acceptance and Commitment Therapy group, and the other 13 mothers were assigned to the control group. The ACT group and the control group completed parenting anxiety scale, Acceptance & Action questionnaire, and mindfulness scale prior to the program and at the termination of the program (and 4 weeks after the termination). Repeated measure ANOVA was conducted on the collected data. The results indicated parenting anxiety of the ACT group decreased significantly more than in the control group and that perfectionism, one of the subfactors of parenting anxiety, significantly decreased; the posttest also showed the effect was maintained. Also psychological acceptance and decentralism, one subfactor of mindfulness in the ACT group, and the effect was also maintained 4 weeks later. This study presented that such findings might be utilized to develop effective programs that could help mothers of preschool and school-aged children by reducing parenting anxiety and increasing psychological acceptance and decentralism with ACT. Finally, implications and limitations of this study were discussed along with suggestions for future studies.