This study aimed to investigate the effectiveness of positive parenting group training for mothers and its effect on children's aggression and social skills. The research method was semi-experimental with a pre and post-test design, a control group, and a 3-month follow-up. Socio-statistics were all mothers of preschool children in district one of Gorgan city in 2018. The sampling method was a multi-stage cluster, in which 2 schools were randomly selected from among preschool schools in district one of Gorgan city. In the next stage, 2 classes from each school and 60 mothers from the statistical community were randomly selected. They were placed in two groups of experimental (30 people) and a control (30 people). The experimental group was trained for 4 weeks, 2 sessions per week, and no intervention was performed in the control group. A follow-up was conducted 3 months later at the end of the post-test. The data were analyzed by covariance analysis and Bonferroni's post hoc test. Based on the results, the positive parenting training program was effective in all four components of aggression and social skills of preschool children (P<0.05). The results showed that positive parenting training has the necessary efficiency to reduce aggression and increase the social skills of preschool children.