The past research have suggested that the Inter-Organizational E-Commerce based on the Inter-Organizational Systems(IOSs) has direct impact on the Inter-Organizational Relationships(IORs) in general. Considering the importance of this issue, however, few empirical research have been conducted. The objective of this study is to examine the impact of the level of Inter-Organizational E-Commerce on the performance of IORs in particular. Reviewing the literature, we suggested a research model and developed ten hypotheses to be tested. We conducted a survey and collected data from 125 companies which were using. EDI systems. The data were analyzed using LISREL 8.30. The major findings are: (1) The volume of E-Commerce has a positive impact on the commitment of trading partners. (2) High quality of information sharing and high degree of standardization improve the trust and the commitment between trading parties. (3) The trust and the commitment are critical precedent variables of cooperation. (4) The more partners cooperate each other, the more transaction cost will be reduced and as a result, the more financial performance will improve. A discussion on the result of the hypotheses test is followed by a discussion on the academic and practical implications of this study.