As many companies are participating in the B2B e-Marketplaces, interests in the business- to-business(B2B) electronic commerce is increasing, E-Marketplace is defined as the virtual market that many players take part in the transaction. E-Marketplace has influenced the manner in which organizational buyers and sellers interact. As a result, it is important to develop an understanding of the behaviors of firms that use these electronic marketplaces. The purpose of this study is to develop a comprehensive model for usage of B2B e- Marketplace and to examine their structural relationships empirically. Drawing from the network theory in interorganizational information system and B2B electronic commerce context, this study identifies trust and commitment, network externality, system integration as the determinants of usage of e-Marketplace. The proposed model is tested using organizational- level survey data from 187 buying organizations that conduct business in MRO e-Marketplaces. The results indicate that network externality, trust and system integration play a strong, central role in determining commitment and usage. The key theoretical contribution of this research is that it begins to extend marketing and interorganizational information system literature in areas such as B2B e-Marketplace. Managerially, this study contributes to the understanding of the role of B2B e-Marketplace providers in internet situation. Limitations of this study and guidelines for future researches are also discussed.