This paper aims at reciprocity between knowledge acquisition and sharing within workgroups. In spite of mandate or volition, knowledge sharing is happened in workplace more or less. In light of favor change, employee will reciprocates knowledge in order to support future exchange. An instable causality between intention and behavior tossed by Fishbein and Ajzen (1980) is explored in the current study that knowledge sharing intention-behavior could be invalid in the case of low knowledge acquisition. Empirical data were collected from 100 three-person groups and valid samples were used to verify our research model statistically. Research results pointed out that reciprocity is critical to knowledge exchange. Particularly, knowledge acquisition not only relates to attitude and intention, but also intervenes in intention-behavior causality.