Abstract Large number of people with Attention Deficit Hyperactivity Disorder during their Adolescence suffer from externalizing problems, aggression and internal conflict, aswell as difficulties in attentional functions and other main problem of this disorder. Therefore, the present study aimed to investigate the effectiveness of Mindfulness-Based Cognitive Therapy (MBCT) on externalizing problems and attention functioning in girls adolescents with ADHD. Method: The present study is a quasi-experimental research with pre-test and post-test design with control group. The participant of the study includes 29 female high school students in district 7 of Mashhad with attention deficit / hyperactivity disorder. Instruments which were used in this study included as follow; SNAP-IV, clinical interview, Achenbach youth self report (YSR) and Selective divided attention software test. The experimental group participated in eight 90-minutesessions of MBCT and the control group was placed on the waiting list. Data were analyzed by multivariate covariance analysis. Results: The results indicated that MBCT not also reduced the main symptoms of ADHD, but also improved attention functioning and externalizing problems in experimental group than the control ones. Conclusion: MBCT led to improving the main symptoms of ADHD, reducing externalizing problems, increasing awareness and attention functioning in girls with attention deficit / hyperactivity disorder.

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