By sharing knowledge, organizations are able to enhance their efficacy, decrease cost of training and moderate risks due to lack of certainty. In the age of knowledge, find a way to motivate employee for sharing knowledge with others is the most difficult issue in term of managing knowledge. Therefore, factors influencing knowledge sharing are particularly vital. This paper was conducted to encompass understanding of the trust and motivational factors that influence knowledge sharing behavior in organizations. It is important that no known study examined the influence of motivational factors onto knowledge sharing behavior through trust as a moderator. In this research we proposed a theoretical framework that combined motivational factors with Theory of Reason Action (TRA) to describe the relations among two types of motivation (extrinsic and intrinsic), trust and worker's intentions and attitudes toward knowledge sharing.