Objective: The study aimed to determine the effects of the anger management program based on cognitive behavioral techniques on adolescents. anger and assertiveness levels. Methods: The study employed an experimental design with pretest-posttest measures and a control group. State-Trait Anger Expression Inventory (STAXI) and Rathus Assertiveness Inventory (RAI) were applied to 9th grade high school students. Fifty-one students who met the inclusion criteria of the study were randomly matched in terms of gender and their scale scores and assigned to experimental and control groups. At the end of the group work, the scales were reapplied to the students both in the experimental group and in the control group. The data was analyzed by SPSS 16.0 statistical package programme and Levene test, t test and chi square test were used. Results: During the first measurement, there was not a statistically significant difference between the STAXI and RAI scores of the experimental and control groups. The measurement conducted with STAXI after the program revealed that the mean scores for the trait anger, anger-in, and anger-out subscales were lower in the experimental group than in the control group, and for the anger control subscale, the mean scores were higher in the experimental group than in the control group and the difference was highly significant. After the program, the mean RAI score of the experimental group was higher than that of the control group, and the difference was statistically significant. Conclusion: The results of this study revealed that the anger management program based on cognitive behavioral techniques decreased students. trait anger levels and helped them express their anger appropriately, manage their anger and develop an assertive behavior.