Socialization is one of the most important goals of any developmental program and educational scientists try to provide students with appropriate contexts to develop socialization throughout the developmental ages. This study aimed to investigate the effect of traditional and modern childish plays on the social development of female students in the first grade (6-7 years old) in 1388-1389 in two elementary schools of regions 13 and 14 of Tehran city. The present research was performed experimentally with groups of modern plays, traditional plays and the control group along with the pretest and posttest. The subjects (N=45) were randomly divided into three groups. The first group played traditional plays for 15 weeks (once a week) and the second group played the modern plays for the same period of time, the third group which was considered as the control group did not carry out any kinds of playing. In order to measure social development of the students, Winelands (1953) social development questionnaire was used to measure social development. In this study, the statistical method of covariance analysis was used to analyze the data. The results showed that both traditional and modern childish plays had an effect on social development of children and there was no significant difference between these two plays, but the traditional plays gained more scores in social development. It can be suggested beneficial to have childish plays in syllabus at schools to improve children’s social development.