The purpose of this study was to investigate the effectiveness of assertiveness skills training on stigma and depression of mothers of Down syndrome students in Isfahan city by semi-experimental method. The statistical population of the study included all mothers of Down syndrome students in Isfahan city in the academic year of 2017-2018. Using available sampling method, 30 people were selected and randomly divided into two groups of 15 and tested. Data were gathered using two internalized stygie questionnaires with a reliability coefficient of 0.89 and Beck Depression Inventory with a coefficient of 0.92. The data were analyzed using descriptive statistics and inferential statistics using covariance analysis. The results of this study showed that assertiveness skill training with a significant level of 0.05 has a significant effect on decreasing the stigma and depression of mothers of Down syndrome students. Finally, we can say that by training assertiveness skills, we can reduce the burden of depression and mothers' depression in Down syndrome students.