The objective of the present research is to study the effectiveness of family drama therapy on reducing parent-adolescent conflict among the adolescents. The research method employed was quasi-experimental study with single subject structure. The sample group was selected through convenience sampling method that included four 12-14-years-old, studying in two Guidance Schools in District 1 of Tehran City during 2014-2015 academic year. The subjects participated in seven family drama therapy sessions and filled the Parent-Adolescent Conflict Measurement Questionnaire (Adolescent Form) three times before the intervention (baseline) as well as during the third, fifth and seventh sessions. Moreover, in order to follow up the trend of changes after the intervention, the results of the research were followed up twice (two weeks and four weeks after the intervention) by the questionnaire. The findings of the research were analyzed through visual analysis graphs, calculate effect sizes and percentage changes The analysis of the findings indicate that family drama therapy was effective in reduction of parent-adolescent conflict in all four subjects. A noteworthy point was considerable reduction of parent-adolescent conflict in the first three sessions. In other words, along with education the positive interactions in the family, improvement of relations, emphasis on the necessity of entertainment in and outside the family and emphasis on the role of father in the family, highest degree of changes in the subject was reported.