Children learn to collaborate with and attract children of their own age, to observe others' rights, to live a team life and to develop many more social processes through play. The present study aimed at investigating the effects of a period of individual and team plays on the social development of educable mentally retarded children. In this quasi-experimental study, two experimental and one control group were used with the pretest-posttest design. The statistical population consisted of mentally retarded students (aged between 8 and 11) in Tehran Province. Two schools were selected from special schools of Tehran Province by cluster sampling method. Then, 45 male students were randomly selected from the students of these schools and assigned to three groups (each group 15 subjects) of experimental (10.7 ± 0.3) and control (10.5 ± 0.4). After the parents' consent, experimental subjects performed the school plays for a month, 12 sessions, and 3 sessions per week. Covariance and Tukey post hoc test were used to analyze the data. The results showed that the mean scores of social development in experimental groups drastically increased in the posttest (P = 0.001). In addition, there was a significant difference in the mean between the experimental and control groups while there was no significant difference in the mean between the team and individual experimental groups (P ˂ 0.001). It can be concluded that team plays in mentally retarded children can lead to their better adaptability and relations in their community. It is suggested that proper facilities should be established for the physical activity of these children and the children should be involved in social interactions so that they can get rid of isolation and loneliness.