We examined victims' perceived responsibility and bystanders' anticipated risk of being victimized themselves when others associate them with the victim (stigma by association, SBA) as possible antecedents of bystanders' helping behaviour towards a victim of workplace mobbing, and explored the effects of gender. Guided by the attribution model of social conduct (Weiner, 2006), a 2 × 2 vignette experiment was conducted. Participants were Dutch regional government employees (N = 161). Path analyses generally supported the hypotheses, but showed different results for women and men. In the strong (Vs. weak) responsibility condition, women reported less sympathy and more anger and men only more anger, which resulted in lower helping intention. Additionally, for men the results showed an unexpected direct positive effect of responsibility on helping intention. Furthermore, in the strong SBA condition, women and men reported more fear and men, unexpectedly, more anger. Consequently, helping intention decreased. The findings on gender are discussed in the context of social role theory, gender and emotion. Our findings suggest that to prevent and tackle mobbing, organizations and professionals should be aware of the attributional and emotional processes and gender differences in bystanders' helping behaviour.