The present study aimed to investigate the effectiveness of group cognitive behavioral therapy in reducing anxiety and depression and glycemic control in children with type I diabetes. The study was quasi- experimental with a pre-test, post-test design with control group. For this purpose, 30 children with diabetes were selected from Imam Reza Hospital in Mashhad. The children were randomly assigned into two experimental group (15) and control group (15). The experimental group was undergone eight 2-hour sessions of cognitive-behavioral training. Before and after the intervention, the Multidimensional Anxiety Scale for Children, which included four components of social anxiety, physical symptoms, harm avoidance, and separation anxiety, and Children Depression Inventory was administrated in both groups. The findings from the covariance analysis test revealed that depression and anxiety and glycemic control in experimental group was controlled at post-test and depression score in experimental group compared to the control group at post-test was decreased. The findings from the multivariate covariance analysis test between components of, physical symptoms, harm avoidance, separation anxiety, and social anxiety revealed meaningful differences between the two groups in social anxiety post-test score. Thus, cognitive behavior therapy can be effective for depression, anxiety, and blood sugar control in children.