The current study aims to examine the mediational effects of explicit weight stigma and moral disengagement (MD) and moderating effects of empathy on the relationship between implicit weight stigma and bullying perpetration. Two hundred and twenty-eight college students (112 men, mean age of 19.89 ± 1.82 years) completed implicit (the Single Category Implicit Association Test) and explicit (the development of the weight stigma scale) measures of weight stigma, and responded to questionnaires regarding MD, empathy, and bullying perpetration. Structural equation modeling was conducted and mediating effects were tested using AMOS 17.0 software. The results indicated that implicit weight stigma significantly predicted bullying perpetration. After controlling for gender, this association was jointly mediated by explicit weight stigma and MD. Furthermore, empathy moderated the relationship between implicit weight stigma and bullying perpetration. Specifically, college students who have high levels of implicit weight stigma and low levels of empathy would score higher on the bully questionnaire. These findings may provide a possible explanation for when and how implicit weight stigma relates to bullying perpetration.