The theories of resource dependence and social network were used to empirically examine the factors influening the focal firms' joining the multi-party alliances against the industry-sponsored e-marketplaces (ISMs).  The results show that the decision of the joining is mainly influenced by two factors: resource dependency and structural centrality in the social network. The higher the resource dependence of a focal firm on the multi-party alliance, the higher its structural centrality in the network, the more likely it will join the multi-party alliance. Thus, both economic and social considerations exist, which influence the strategic choices of focal firms jointly.