Abstract In the competitive business environment, knowledge sharing among the members of organization is very important. One is willing to share oneself knowledge to others, is based on “ trust “. “social support“ is an important factor of trust . Therefore, this study was to examine the effects of social support on knowledge sharing, and the mediate effect of trust among the social support and knowledge sharing. The study adopted questionnaire survey method. A total of 550 salespersons were selected by proportional stratified sampling method. Using descriptive statistical analysis, multiple regression analysis, multiple hierarchical regression analysis of data analysis. The results showed that social support has significant effect on knowledge sharing, and trust is explicitly shown to mediate the relationship between social support and knowledge sharing.