<p id=C2>Narcissism is a personality trait characterized by an inflated self-image, a strong sense of psychological superiority and entitlement, and a low level of empathy. As narcissism has a substantial impact on employees’ work quality, happiness, satisfaction, and interpersonal relationships, employee narcissism has become an important topic of research among scholars and management practitioners, who have called for further research on the behavior of narcissistic employees in the process of interpersonal interaction. However, research on the impact of employee narcissism on prosocial behavior has reached inconsistent conclusions; thus, the mechanisms by which employee narcissism affects prosocial behavior need to be further explored. To fill this theoretical gap, we drew on the Narcissistic Admiration and Rivalry Concept (NARC), and hypothesized that employees’ narcissistic admiration has a positive impact on prosocial behavior via relational approach motivation and that narcissistic rivalry has a negative impact on prosocial behavior via relational avoidance motivation. We further expected task interdependence, as an important situational factor, to directly influence employees’ expression of different narcissistic traits and motivation and their subsequent prosocial behavior. <break/>We tested these hypotheses in a field sample of 235 employee-colleague dyads using a time-lag research design. The data were collected by administering the Narcissistic Admiration and Rivalry Scale, the Approach and Avoidance Scale, the Task Interdependence Scale, and the Prosocial Behavior Scale. At Time 1, we collected the employees’ demographic variables (gender, age, and educational background) and asked them to rate their narcissistic admiration, narcissistic rivalry, and task interdependence. At Time 2 (approximately one month after Time 1), the employees rated their relational approach motivation and relational avoidance motivation, and their colleagues were asked to rate these employees’ prosocial behavior. We applied confirmatory factor analysis, descriptive statistics and correlation analysis, path analysis, and bootstrap methods using SPSS 24.0 and Mplus 7.4 to analyze the data from the 235 employee-colleague pairs. <break/>Confirmatory factor analysis was performed to examine the discriminant validity of the key variables (i.e., narcissistic admiration, narcissistic rivalry, task interdependence, relational approach motivation, relational avoidance motivation, and prosocial behavior), and the results confirmed discriminant validity. Next, we used path and bootstrap analyses to test the hypotheses. The results were as follows: (1) narcissistic admiration had a significant positive impact on employees’ prosocial behavior; (2) narcissistic rivalry had a significant negative impact on employees’ prosocial behavior; (3) relational approach motivation mediated the relationship between narcissistic admiration and prosocial behavior, however, relational avoidance motivation didn’t mediate the relationship between narcissistic rivalry and prosocial behavior; and (4) task interdependence played a moderating role in the relationship between narcissistic admiration and relational approach motivation and further moderated the indirect effect of narcissistic admiration on employees’ prosocial behavior via relational approach motivation. <break/>This study makes several contributions to the literature on narcissism. First, it explores the double-edged effects of narcissistic admiration and narcissistic rivalry on employees’ prosocial behavior, thereby helping scholars better understand these traits. It also explains the inconsistent results of previous studies on the relationship between employee narcissism and prosocial behavior. Second, based on the concepts of narcissistic admiration and narcissistic rivalry, this study explores the mechanisms of both traits on employees’ prosocial behavior. Although the mediating role of relational avoidance motivation was not significant, this gives us another important insight that future researches can try to independently examine the influence effects, mechanisms, and boundary conditions of narcissistic admiration and narcissistic rivalry without being overly tied to the NARC framework. Third, by integrating trait activation theory, this study investigates the important role of a situational factor (i.e., task interdependence) in the relationships between narcissistic admiration, narcissistic rivalry, and employees’ prosocial behavior, which can help organizational managers better understand the roles of narcissistic admiration and narcissistic rivalry.