One of the assumptions of the triadic reciprocal model is that the dynamic relationships between internal factors and environmental contexts may have a reciprocal influence on behaviour. Based on this assumption, this study examined whether callous-unemotional traits mediate the relationship between family competence and bullying among 256 selected senior secondary pupils (age = 14–16; M = 15.5, SD = 5.4; boys = 131 and girls = 125). Three self-report scales were used to collect data for bullying, family competence, and callous-unemotional traits. Mediated multiple regression was used to test the hypotheses. The result showed that callous-unemotional traits and family competence have a positive and negative linear relationship with bullying, respectively, B = 0.13 and −0.20, p < .01. Similarly, the indirect effect of family competence on bullying through callous-unemotional traits was significant, B = 0.04, p < .05. This indicated that callous-unemotional traits could regulate the effect of family competence on bullying. The results may have implications for understanding, planning, and designing programmes for preventing and intervention of school bullying.