The objective of the current study was to investigate the role of personality traits in predicting cyber-bullying in second year high school students in Zanjan. This is a descriptive correlational study. The statistical population included all boy and girl high school students in Zanjan. Considering the 15500 students in the population, the sample size turned out to be 348 based on Krejcie and Morgan formula. The sample was selected through convenience sampling method using virtual social networks. To collect data, NEO Five-Factor Inventory (NEO-FFI) and Cyber-Bullying/ Victimization Experiences Questionnaire (CBVEQ) were used. Data analysis was performed through Pearson correlation and stepwise multiple regression using SPSS software (version 25). The results showed that the relationship of neuroticism and openness to experience with cyber-bullying and cyber-victimization was significant and positive. In addition, the relationship of agreeableness with cyber-bullying and cyber-victimization was significant and positive. Furthermore, from among personality traits, neuroticism and agreeableness could predict cyber bullying (β = 110); neuroticism could also predict cyber victimization (β = .117). In general, the results indicated that when neuroticism and agreeableness increased, cyber-bullying and cyber-victimization also increased. This finding can be a guide for counselors and psychologists to prevent and reduce cyber-bullying and cyber-victimization
