Facilitating employees' knowledge transfer to colleagues is a critical, yet challenging task. This study suggests that an individual's social networks and motivational factors facilitate knowledge transfer based on the social capital theory and the theory of collective action. More importantly, this study also proposes that the facilitating effects of social networks and motivational factors differ depending on the different modes of knowledge transfer, namely, the closed (one-to-one) and the open (one-to-many) modes. By analysing 325 survey responses of eight research and development groups from five firms with structural equation modelling, we found that network centrality and organizational reward were influential only on open knowledge transfer while expected reciprocity was influential only on closed knowledge transfer. On the other hand, average strength of ties and intrinsic motivational factors such as group identification and self-efficacy seemed to affect both types of knowledge transfer. Additionally, the facilitating effects of social networks were found to be partially mediated by motivational factors.