Computer-based systems operating between two or more co-operating organizations as part of their business relationship are generally referred to as inter-organizational systems(IOS). IOS automates aspects of transactional work between organizations and coordinate other activities. These systems facilitate organizational interaction as well as flows of materials, services and information. This planning provides as business direction for IOS applications, coordinates the efforts of participants, and deals with technical and non-technical IOS issues. This paper seeks to research the effect of strategic determinants of IOS to the efficiency of IOS. The determinants that selected from prior researches are top management support, is support and vendor/consultant support. The results show that the effect of top management support to efficiency of IOS was significant and this effect mediates the effect of other factors.