This paper investigates the positive influence of perceived organizational support (POS) on employees' knowledge sharing behavior through their affective commitment. Moreover, it examines the moderating effect of task interdependence, as a situational factor, on this mediating relationship. The results from a total of 222 supervisor-subordinate dyads showed that POS was positively related to affective commitment, leading to knowledge sharing behaviors. Besides, the mediation effect of affective commitment was stronger when task interdependence was low than when it was high. These results imply that employees receiving high organizational support would share their knowledge when they perceive knowledge sharing as a voluntary behavior. Theoretical and practical implications are discussed.