Background: Internet Gaming Disorder poses a serious threat to adolescent's physical and mental health. Cognitive-behavioral therapy (CBT) is a promising intervention for treatment and management of such problem. Objective: Assess the effect of cognitive behavioral therapy on the internet gaming disorder and quality of life among preparatory school students in Alexandria. Settings: The study was carried out at 4 randomly selected governmental preparatory schools in Alexandria. Subjects: All students in the first and second grades in the previously selected settings (2080 students) were screened using internet gaming disorder scale. 200 students with internet gaming disorder from the previously selected schools were randomly selected to assess the effect of CBT application. Tools: Three tools were used for data collection. The first tool was students‟ basic data structured interview schedule. The second tool was Internet Gaming Disorder Scale (IGD-20). The third tool was Ped Quality of Life Inventory Short Form (Peds QLTM – SF 15). Results: More than one tenth (12.7%) of the studied students had internet gaming disorder. Immediately, after the program application around one third of them had no disorder and increased to 48.5% in the follow up phase. Before the program application, 37.0% of them had good quality of life, raised to 60.5% and 51.5% in the immediate evaluation and in the follow up phase respectively. Conclusion and Recommendations: Internet gaming disorder is a prevalent problem among adolescents that affect their quality of life and CBT is an effective intervention 2 in managing such problem. The study recommended regular screening and early interventions and monitoring of internet use either by self or involving family members.