The original study investigated sex differences in the relationships between multiple forms of peer victimization (physical victimization, verbal victimization, and social exclusion) and subtypes of aggression (reactive aggression and proactive aggression) in schoolchildren. A self-report questionnaire assessing levels of peer victimization and aggression was administered to 3790 schoolchildren (1916 males and 1874 females) aged 11 to 17 (M = 13.19; SD = 1.17) from 10 middle schools in Hong Kong. The pure effect of each subtype of aggression were evaluated by statistically controlling for another subtype of aggression in analyses. Furthermore, participants were classified as non-aggressors, reactive aggressors, proactive aggressors, and reactive–proactive aggressors to investigate their differences in specific forms of peer victimization. Data were analyzed by hierarchical linear regression and ANOVA. The results showed: (1) Sex significantly moderated the relationship between specific forms of peer victimization and subtypes of aggression; (2) In males, reactive aggression was positively predicted by verbal victimization; proactive aggression was positively predicted by physical victimization and social exclusion, and negatively predicted by verbal victimization; (3) In females, reactive aggression was positively predicted by physical victimization and social exclusion; proactive aggression was negatively predicted by social exclusion; and (4) Reactive–proactive aggressors reported more physical victimization than other types of aggressors. The findings have significant implications for distinctive functions of reactive and proactive aggression and the need to develop differentiated interventions for male and female schoolchildren.