Despite the increasing body of research on workplace incivility, the relationship between supervisor incivility and employee job performance, as well as its intermediary mechanisms, has received relatively little attention from researchers. Drawing on the transactional model of stress and self-determination theory, we propose employees' job insecurity and amotivation as mediating mechanisms between supervisor incivility and employee job performance. The proposed serial-mediation model was tested through a multilevel analysis of two-wave surveys collected from kindergarten teachers and their principals. Our mediation analysis revealed that incivility perpetrated by kindergarten principals exerted a negative effect on teachers' job performance three months later by shaping job insecurity perceptions and amotivation. These findings have theoretical implications for the workplace incivility literature and managerial implications for practitioners.