This study examined the factor that promote the subordinate’s knowledge sharing as a source of competitive advantage of organizations. This study was conducted with the following three research objectives. First, we would like to present the value of leader humility that promotes knowledge sharing by empirically confirming that relationship. Second, we investigated the mediating role of the loyalty to supervisor in the impact of leader humility on knowledge sharing. By doing so, we would like to find the specific process of influence of leader humility. Third, we examined the boundary conditions of leader humility effects by checking leader expertise as a factor that can control the impact of leader humility. A survey was collected data from military members in the Navy, Republic of Korea. A total of 196 matched dyadic data was used for analysis. Major findings of the study are as follows. First, based on the social exchange theory, the results showed the positive relationship between leader humility and knowledge sharing. Through this, we demonstrated the leadership function of leader humility. Second, based on social exchange theory and implicit leadership theory, the effect of leader humility on knowledge sharing was mediated by subordinates’ loyalty to supervisor. This results provided a lesson on why leaders should show humility to increase employee’s knowledge sharing. Finally, this results supported the moderated mediation hypothesis, verifying that the magnitude of the indirect effect was changed by the level of leader expertise. This suggests that leaders need to be both humble and competent to be effective. In the last section, we discuss the limitations and the future direction of the study.