The purpose of this research was to Study of Effectiveness of Mindfulness on decreasing marital stress in Attention Deficit/ Hyperactive Disorder children's mothers. The design of the study was quasi-experimental, and of pretest- posttest with control group kind. The statistical population comprised mothers of children with attention deficit hyperactivity disorder (ADHD) referred to houses of health in No. 21 of Tehran municipality. The research sample consisted of 24 mothers that were selected by the available sampling method and randomly assigned to experimental and control groups. ADHD assessment scale and Marital stress scale were used to gather data. The experimental groups received 8 eight two-hour sessions of mindfulness each week while the control group received no specific intervention. At the end, both were re-evaluated (post-test). Data were analyzed by analysis of covariance (ANCOVA). The results indicate that mindfulness training on aritalm stress of mothers of children with ADHD was significantly effective and mothers of the experimental group showed significant reduction (p<0.05) in marital stress. According to these findings, mindfulness training is recommended to be used for reduction of stress marital and improving of mental health in mothers of children with ADHD.