Attention Deficit/ Hyperactivity disorder is a common problem in childhood that continue through adolescence and adulthood. Affect the various aspects of one's life. Because several treatment models designed to draw the disorder .The purpose of this research was to Study of Effectiveness of Mindfulness on decreasing clinical signs  in Attention Deficit/ Hyperactive Disorder children. The design of the study was quasi–experimental, and of pretest- posttest with control group kind. The statistical population comprised children with attention deficit hyperactivity disorder (ADHD) referred to psychological  clinics .of Tehran municipality. The research sample consisted of 30 child  that were selected by the available sampling method and randomly assigned to experimental and control groups .IVA  scale and CBCL scale were used to gather data. The experimental groups received 8 eight 90 minutes 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 multi  covariance (MANCOVA).The results indicate that mindfulness training on clinical signs of children with ADHD was significantly effective and children of experimental group Showed  significant reduction (p < 0/001) in clinical sign. And co morbid disorder such as anxiety ad affective problem and oppositional defiant disorder  reduced  significantly.  According to these findings,mindfulness training is recommended to be used for reduction   and improving clinical signs of children with ADHD.