The present study was undertaken to investigate the effectiveness of group parenting training for mothers based on acceptance and commitment in reducing the symptoms of externalizing disorders in children. This quasi-experimental study had a pretest-posttest control group design with a follow-up session. The statistical population of the study consisted of mothers of children aged 6-8 referred to Omid Children's Counseling Center in Tabriz in the autumn and winter of 2017. The children were diagnosed to have symptoms of externalizing disorders using the Child Behavior Checklist (CBCL) Achenbach-Parents’ version. Twenty-four mothers were selected using convenience sampling method and were randomly assigned to experimental (N=12) and control (N=12) groups. The experimental group was subjected to parenting training for eight 2-hour sessions, while the control group did not receive any intervention. Data were analyzed using ANCOVA. The results showed that in the posttest stage, there was a significant difference between the mean scores of the experimental and control groups after eliminating the effect of pretest (F=72.732, P<0.05). Furthermore, the results revealed that in the follow-up stage, there was a significant difference between the mean scores of the experimental and control groups after eliminating the effect of the pretest (F= 43.895, P<0.05). Therefore, it can be concluded that parenting training for mothers based on acceptance and commitment is effective for reducing the symptoms of externalizing disorders in children and this effect is stable over time. It is suggested that this program be used in counseling centers.