PurposeTrust, as one of the core components of a relationship, has attracted research attention from many disciplines. From the perspective of IT outsourcing, this paper aims to divide trust into two levels, interpersonal trust and interorganizational trust, and explore the effects of these two levels of trust on knowledge sharing and IT outsourcing success.Design/methodology/approachBased on social exchange theory and the theory of organization boundary systems, a theoretical model was developed and tested empirically with the responses to a cross‐sectional survey. Data were collected from key informants of 143 firms that had outsourced at least part of their IT functions.FindingsThe data analysis results showed that interpersonal trust plays a more dominant role than does interorganizational trust in making IT outsourcing successful and the extent of knowledge sharing has a significant mediating effect between interpersonal trust and IT outsourcing success.Originality/valueFrom the managerial perspective, findings from this study once again emphasize the importance of relationship management (trust and knowledge sharing) on overall IT outsourcing success. Paying attention to interpersonal trust is an effective way for an organization to build and maintain a successful IT outsourcing relationship with its service provider.