Background: Play therapy is a structured approach based on therapy theories that establish children's learning and communication processes.  Objectives: The purpose of this research was to investigate the effectiveness of play therapy on anxiety and shyness of elementary school children. Methods & materails: This pre-test post-test with a control group design was conducted on students of both sexes studying at Rezvan Khutbehsarai Elementary School in the academic year 2020-2021, in Talesh, North of Iran. Students who had a high score on anxiety and shyness test were selected by purposive sampling method and then randomly allocated into experimental and control groups. Anxiety and shyness were assessed using Spence Children's Anxiety Scale and Children's Shyness Questionnaire. Cognitive-behavioral play therapy intervention was performed during ten sessions. Data were analysed using analysis of covariance. Results: Play therapy significantly decreased the mean score of shyness and anxiety in the experimental group. The adjusted post-test mean score of anxiety (52.13, SD= 3.775) and shyness (77.88, SD= 5.947) in the experimental group was significantly lower than the adjusted post-test mean score of anxiety (61.42, SD= 3.671) and shyness in the control group (94.11, SD= 4.332).  Conclusion: The finding showed effectiveness of cognitive behavioral therapy in reducing anxiety and shyness in elementary school students. Parents should be motivated to learn concepts such as the need for play, types of games, and the role of play in repairing the parent-child relationship.