Trying to reduce clinical problems in children autism through education of parents in recent years has been addressed by researchers. This study aimed to investigate the effectiveness of training of pivotal response treatment (PRT) to mothers with 6 to 12 year old autistic children on reducing the autism symptoms. Also, the impact of PRT on reduction of parenting stress was addressed in this study. In a clinical trial work, 14 mothers of autistic children in a rehabilitation clinic for autistic children in Tehran city, selected. They were randomly assigned to intervention and comparison groups. The intervention group received treatment programs in addition of routine programs of clinic within 12 training sessions. The Autism Evaluation Treatment Checklist (Rimland and Edelson, 2005) and Parental Stress Questionnaire (Berry and Jones, 1995) were used for measuring autism symptoms and parenting stress, respectively. The results of covariance analysis revealed that this treatment method is effective in reducing the parental stress of mothers of autistic children (P ≤ 0.01). Furthermore, this method resulted in an improvement in communication abilities, social interaction, cognitive-sensory ability, and behavior of autistic children (P ≤ 0.01).