This research focuses on relational and contractual mechanisms and examines their impact on service suppliers’ acquisition of tacit and explicit knowledge from Multinational Corporations in international outsourcing. Based on a theoretical analysis and an investigation into 232 service providers operating in China via questionnaire and empirical study, it is found that: Firstly, relational mechanisms (trust, cooperation and guanxi) have a positive effect on the acquisition of tacit and explicit knowledge, and guanxi shows the most important effects. Secondly, contract mechanisms relate positively to effect on the explicit knowledge acquisition and negatively to the acquisition of tacit knowledge. Thirdly, relational and contractual mechanisms have a positive, collective effect on service suppliers’ explicit and tacit knowledge acquisition.