There have been quite many studies to identify factors affecting successful implementation of EDI systems. However, previous studies have investigated influencing factors independently. Given the complexity involved in the implementation of EDI systems, it might be quite necessary to investigate the interaction effects between influencing factors. The primary purpose of this study is to investigate the interaction effects of organizational characteristics as contextual variables on the relationship between managerial characteristics and EDI implementation. Analysis of 202 responses of survey questionnaire indicates the following: 1) Education/training and top management support has positive effect on the successful EDI implementation. 2) The degree of decentralization has strong, and management risk position has mild moderating effect on the relationship between managerial characteristics and EDI implementation. 3) The degree of formalization and organizational size have no moderating effect. 4) The subgroup analysis, conducted to determine the exact nature of interaction effect, reveals that the relationship between managerial characteristics and EDI implementation is significantly stronger with a high level of decentralization or management risk position than with a low level.