Background: The aim of this study was to evaluate the effectiveness of assertiveness training in reducing the addiction potential of eleventh grade male students in the city of Hamadan.

Materials and Methods: This was an experimental study with pretest-posttest design. From Boy's High Schools of Hamadan participated in this study, one school was selected by the cluster sampling method and 40 people were randomly selected and were replaced in a test group and a control group (n = 20 subjects, per group). Assertiveness training for 8 sessions were conducted in the first group while the control group was on the waiting list.

Results: Data were analyzed using analysis of covariance. Descriptive statistics showed that scores of the experimental group had decreased, compared to the control group and post-test showed that the value of F for the preparation of active addiction was 1076.7 and for passive readiness to addiction was 2608.4 which is significant in the level of (P<.001).

Conclusion: The analysis of covariance showed assertiveness training could significantly decrease the scores of experimental group compared to the control group in both dimensions of the addiction potential.