Bystanders can affect workplace bullying by engaging in active or passive behaviours. However, there is a knowledge gapregarding how perceived work environment factors relate to bystander behaviour. The study aim was to investigate how job demands, and job resources are associated with bystander behaviour in workplace bullying. An online questionnaire wasdistributed to a sample of health care workers at two time points. Longitudinal data were obtained from 1144 respondents. Cross-lagged panel models were used to investigate associations between job demands, job resources, and bystander behaviours over time. The results showed that social support was positively related to active behaviours, whereas influence at work was negatively related to both active and passive behaviours. Perceived illegitimate tasks were negatively related to active and positively related to passive behaviours, whereas emotional demands had an unanticipated opposite pattern of relationships. The findings provide new information about how factors in the organisational and social work environment are associated with active and passive bystander behaviours in workplace bullying. Specifically, the results expand current understanding of workplace bullying by relating bystander behaviour to the organisational context.