Abstract: The study investigated the relationship between job stress and Counterproductive Work Behaviour (CWB) and the moderator effect of negative affectivity on the relationship. Measures of job stress, negative affectivity and counterproductive work behaviour were administered on 422 secondary school teachers randomly selected from southwest Nigeria. Data were analyzed using hierarchical multiple regression. Job stress and negative affectivity were positively correlated with CWB. Negative affectivity moderated the relationship between job stress and CWB such that high levels of CWB occurred when job stress and negative affectivity were both high. The clinical implication of providing counselling interventions for reducing negative affectivity and facilitating positive affectivity and removal of stress from the researchers environment by employers were discussed.