Background : Bullying is an emerging risk factor for poor mental health outcomes adversely affecting children and adolescents. However, it has rarely caught the attention of the health and education sector due to lack of evidence in many countries including Nepal. The aim of this study was to assess the prevalence and factors associated with bullying behavior among adolescent students in Nepal.Methods : We used nationally representative data from the Nepal Global School-Based Student Health Survey that involved two-stage cluster sampling design with the use of a standard set of self-administered questionnaires. Complex sample analysis was done to determine the prevalence and correlates of bullying among 6529 students of 68 schools studying in grade 7 to 11 using descriptive analysis and multivariable logistic regression.Results : The overall prevalence of bullying among Nepalese school adolescents was 51% (55.7% in male and 46.1% in female). Bullied adolescents more commonly reported mental health problems with higher risk of loneliness (aOR 1.39, 95% CI: 1.14, 1.69), anxiety (aOR 1.97, 95% CI: 1.57, 2.47), suicide attempt (aOR 1.99, 95% CI: 1.48, 2.67), school absenteeism due to fear (aOR 1.72, 95% CI: 1.36, 2.19) and school truancy (aOR 1.43, 95% CI: 1.14, 1.79). A significant association was seen between bullying victimization and negative health behaviors like involvement in physical fights (aOR 3.70, 95% CI: 3.00, 4.56) and tobacco use (aOR 1.99, 95% CI: 1.09, 3.61).Conclusion: School bullying is significantly associated with mental health factors like loneliness, anxiety, suicide attempt, school absenteeism and risky behavioral factors like smokeless tobacco use and involvement in physical fight. The insights provided by these findings have important implications for planning anti-bullying strategies in school settings in the Nepalese context.