The study aims at identifying the widespread of cyberbullying phenomenon among university students; the sex differences in irrational beliefs, mental resilience, and cyberbullying; the study three-value relationship; the contribution of irrational beliefs, mental resilience to cyberbullying prediction for university students. The study sample consists of (486) male and female university students: (224 males) by 46,1%, (262 females) by 53,9% at faculties of medicine, engineering, agriculture, specific education, arts, and law. Their ages are (18-21) years old, with an average of (19,29) years old, and a standard deviation at (1,037). The study tools contains three scales which are: irrational beliefs scale, cyberbullying scale (prepared by the both researchers), and mental resilience scale (prepared by Salah Sherief Abd El Wahab, 2011). Some statistical methods are used such as: T-test, correlation coefficient, regression analysis. The study results ends with:The existence of differences of statistical significance among the marks of students in cyberbullying and postulated mean’s score is 102,5. This means that cyberbullying exists moderately among the sample, The existence of differences of statistical significance among the mean of Zagazig university students’ marks (males-females) in irrational beliefs scale and cyberbullying scale for the sake of males. There is no differences between males and females in mental resilience scale, The correlation coefficient results show relations of statistical significance among irrational beliefs, mental resilience, and cyberbullying as follows: cyberbullying correlates positively with irrational beliefs and mental resilience, The results of the regression analysis of independent values (irrational beliefs) on cyberbullying are significant at 0.01, with relative contribution of these values by 30%; whereas the results of the independent values (adaptive resilience - automatic resilience) on cyberbullying are significant at 0.01, with relative contribution of these values by 78%.