This research aimed to investigate the effectiveness of the theory of mind training on decreasing the aggression and on increasing the ability of the theory of mind in preschool children. The research design of the study was of type Quasi-experimental with pre-post test. 34 children (with symptoms of aggression) were randomly assigned into two groups. The experimental group received the interventions related to the theory of mind during 9 sessions. Research tools of the study included the aggression questionnaire, developed by Vahedi et al, and the false-belief test to assess the children’s theory of mind. Data was analyzed using ANCOVA. According to the findings obtained from the analysis of ANCOVA, interventions related to the theory of mind caused an increase of the ability of the theory of mind and a decrease of the aggression among the experimental group in comparison to the control group. Considering the results of the study it can be said that the theory of mind training can cause an increase of the ability of the theory of mind and a decrease of aggression. Therefore, in the parents – child context and also in the kindergartens the theory of mind training should be considered and emphasized.

Keywords: aggression, theory of mind, child