Despite previous research suggests that ethical leadership stimulates employees’ ethical and prosocial behaviors, still little is known about when ethical leadership may be more (vs. less) effective in promoting employee knowledge sharing, a generous and ethical behavior of “donation” in the knowledge management domain at work. Drawing on career development perspective, the current study tested a mediated moderation model in which career age moderates the ethical leadership-knowledge sharing relationship through career plateau. Using multi-wave and multi-source data from a sample of 301 employees in an information technology company, results demonstrated that career age was positively related to career plateau, which in turn moderated the relationship between ethical leadership and employee knowledge sharing, such that the relationship was weaker for employees with high levels of career plateau.