The purpose of this research is to investigate the effectiveness of dialectical behavior therapy on cyber bullying in second year high school students. It was a quasi-experimental study with a pretest, posttest, control group, and three-month follow-up period design. The statistical population included second period high school students in the city of Isfahan in the autumn of academic year of 2022–2023. The research tool was cyber bullying/victimization experiences questionnaire (CBVEQ) (Antoniadou, Kokkinos and Markos, 2016). Based on the scores obtained, 30 people who scored higher than 30, were selected by available sampling method and randomly divided into two groups. Dialectical behavior therapy was applied to experimental group in eight 90-minute sessions, while the students in the control group didn’t receive such intervention during the study. The data were analyzed through ANOVA repeated measurement via SPSS-26 software. The results showed that dialectical behavior therapy had an effect on cyber bullying in second year high school students in the experimental group at the post-test stage and these changes were statistically significant (p<0/05). Findings showed that dialectical behavior therapy reduces direct and indirect cyber bullying behaviors in teenagers.