Objective: The present study was conducted to determine the effectiveness of positive psychotherapy on stress in mothers of children with intellectual disability. Method: In this study, 30 mothers of children with intellectual disability were selected and then randomly assigned into equal experimental and control groups. The assessment instrument was the Parental Stress Scale. First, questionnaires were administered as the pretest and then positive psychotherapy was offered to the experimental group in eight two-hour sessions. At the end of the course, participants were reevaluated using the Parental Stress Scale. Data were analyzed using MANOVA. Results: The results indicated that positive psychotherapy successfully reduced stress for both domains of parent and child in mothers of children with intellectual disability. Conclusion: Overall, it can be said that positive psychotherapy can effectively decrease stress and can thus be used to help the mothers of children with intellectual disability.