Purpose - In China, online intermediaries have become increasingly influential in the last few years, notably in the business-to-business (B2B) domain. However, little research has considered the impact of these intermediaries on either the tacit knowledge or the guanxi that are so central to Chinese business processes. In this paper, authors investigate this impact, as well as the consequent shifts that are taking place on B2B platforms, focusing on the case of Alibaba, China's largest online business intermediary. Design/methodology/approach - An exploratory case-study approach is employed in this paper. The authors have comprehensive investigated Alibaba's trading platforms and associated technologies. They have also engaged 15 Alibaba users (buyers and sellers) from seven different countries/territories in semi-structured interviews and use the interview data to supplement the own findings. Findings - Alibaba is effectively functioning as a substitute for traditional, offline social networks. In the process, it is leveraging and disseminating explicit knowledge critical to all aspects of the purchasing/procurement process, as well as changing the role of guanxi throughout the business purchasing/procurement process. Alibaba is thus engineering radical changes in the way business can be conducted in China. Research limitations/implications - Experienced researchers of Chinese management have traditionally been wary of ignoring cultural norms, which, in this case, would highlight the importance of both guanxi and tacit knowledge. The shift from tacit to explicit knowledge representation, coupled with a modified role for guanxi, is thus rather unexpected and should lead researchers to query previous assumptions, as well as test new ones, specifically in the area of online B2B transactions, but potentially in other domains where online communications are involved. Practical implications - Chinese business people are all too aware of the importance of tacit knowledge and guanxi. The potential for this tacit knowledge to be represented explicitly online, coupled with the shifting role that guanxi may play, should be of great interest to those who wish to explore the online marketspace. It may be particularly attractive to newcomers (notably non-Chinese) to the Chinese market since their own tacit knowledge and guanxi may be less well developed and they may be in a better position to leverage the online platforms. Originality/value - There is little prior work on Chinese B2B e-commerce from a guanxi-based or knowledge management (KM) perspective that builds on the experiences of online buyers and sellers. They chart this area and seek to integrate the two disparate streams of research on guanxi and KM in the context of B2B e-commerce. © Emerald Group Publishing Limited.