With the progress of IT, the strategic use of information systems (IS) has been applied to the inter-organization business areas, that is called Inter-organization Systems (IOS). Previous IT diffusion researches or IT adoption researches have been focused to newly emerged IT but confined into individual organization. However, IOS such as internet relates with between organizations. In this sense, this research has analysed the IT diffusion factors affected by IOS based on the previous studies of IT adoption. This study employed a research model using the factors of adopting IOS in organization, and conducted an empirical research with questionaries with top domestic 80 firms. And the finding is that the factors of the CIO support, business partners and an industry community have significance but other factors such as the size of firm, the degree of IS maturity, the degree of firm centrality, the complexity or suitability of IOS does not.