Emotional-behavioral problems are common in preschool-children and might have some destructive effects on them as well as others. Sand tray therapy is an effective technique that encourages children to express their thoughts, feelings, and conflicts through symbolic expression and story. In this technique a person has an opportunity to resolve conflicts, remove obstacles, and gain acceptance of self. The purpose of this research was to determine the effect of sand tray therapy on reducing emotional-behavioural problems among preschool children. A randomized controlled trial method was applied in this research. The statistical population consisted of preschool children who suffered from behavioural-emotional problems in Tehran in 2016. Three centers were randomly selected from preschool centers in Tehran. The scale of Child Behaviour Checklist (CBCL) was completed by parents. 24 children whose scores placed between the boundary range of 65<T69 were identified and they were randomly assigned to experimental and control groups (12 in per group). The experimental group was individually treated using the sand tray, but the control group did not receive any treatment. ANCOVA test was used for data analysis by SPSS 22. The results showed that sand tray therapy could reduce anxiety/depression and social problems (in the area of emotional problems) and aggression (in the area of the behavioral problem) in preschool children significantly. According to the results, it is recommended that child psychologists apply the sand tray therapy for reduction some of emotional-behavioural problems such as anxiety, depression, and social problems in preschool children.