We constructed a research model based on the social cognitive and social exchange theories to investigate the relationship between supervisor narcissism and employee prohibitive voice. We focused on the mediating role of employee voice efficacy and the moderating role of supervisor–subordinate guanxi. We recruited enterprise employees in China and their direct supervisors (231 supervisor–subordinate dyads) as participants, who completed a 2-wave survey. The results showed a significantly negative relationship between supervisor narcissism and employee prohibitive voice, and the relationship was mediated by employee voice efficacy. Supervisor–subordinate guanxi negatively moderated the relationship between supervisor narcissism and employee voice efficacy. Thus, organizational executive staff should manage conditions to reduce the negative influence of supervisor narcissism, thereby promoting employee prohibitive voice.