Purpose: The present study was conducted to investigate the effectiveness of teaching the Picture Exchange Communication System (PECS) on mothers’ stress and its effectiveness on the child-parent relationship, communication and social skills of slow-paced non-speaking children. Method: The current study was a single-subject quasi-experimental type with an A-B design. The statistical population of the present study was made up of all slow-paced non-speaking students in Shahrood city studying in the academic year 2021-2022 which was obtained using available sampling method, and finally 3 children were selected (one male and two female students). The sample group was subjected to the educational program of the Picture Exchange Communication System (PECS) for 18 sessions. The tools of this research included Age and Stages Questionnaire (ASQ-3), Gilliam Autism Rating Scale (GARS-3), Child-Parent Relationship Questionnaire (CPRQ) and Parental Stress Questionnaire (PSS). The data were presented in the form of tables, graphs and descriptive reports. Findings: The findings showed that in the stages of post-test 1, post-test 2 and follow-up (one month apart), the educational program was effective on the child-parent relationship, communication and social skills of slow-paced non-speaking children and their mothers’ stress level. Conclusion: It can be concluded that the educational program of the Picture exchange communication system is effective on social and communication skills, so it is necessary that the educational program of the Picture exchange communication system receives the attention of therapists and researchers.