Background: The estimated prevalence of mental health disorders in children and adolescents is between 10% and 20%. Furthermore, a quarter of very premature infants exhibit socioemotional delays in infancy and childhood. The objective of this study was to determine the validity and reliability of Greenspan social-emotional growth chart (GSEGC) in Persian children aged 1-42 months. Materials and Methods: After translation procedures, the face validity, content validity, construct validity, test-retest reliability, and internal consistency of the GSEGC questionnaire were evaluated. The quality of translating items was obtained using the suggestions of the research group. The face validity of the GSEGC was performed by interviewing with 10 mothers in the target group. To evaluate content validity quantitatively, content validity ratio (CVR) and content validity index (CVI) were used after reviewing the face and content validity and pilot study, 264 parents of children aged 1-42 months completed the GSEGC questionnaire to assess the construct validity and internal consistency. In order to determine the test-retest reliability, after 2 weeks, 18 parents completed the questionnaire again. Results: Eleven questions were changed according to the interviews (questions 1-6, 9-11, and 15-16). The lowest CVR was related to items 30 and 20 (0.636), and other items had an acceptable CVR. The lowest CVI value was related to item 1 of clarity and simplicity (0.818), and other items had an acceptable CVI. Intra-class correlation coefficient was 0.988 for all items of questionnaire. Furthermore, Cronbach's alpha coefficient was 0.952 for all items. In factor analysis, two factors were extracted from the items in questionnaire. Conclusion: The Persian version of GSEGC questionnaire has acceptable face, content and, constructs validity, test-retest reliability and high internal consistency in the target population. Therefore, the Persian version of the GSEGC can be used as a tool to assess 1-42 months sensory processing and socio-emotional development.