This study presents the growth strategy of outsourcing service by finding out the differences of importance between user firms and system integration(SI) firms in Korean outsourcing business, The result of data analysis reveals that there are siginificant differences between user firms and SI firms in some components of information systems(IS) outsourcing services. User firms regarded integation of distributea data centers as the prominent issue of IS environment changes. Meanwhile, SI firms chose management of IS/VAN center, office automation(OA), and management of global network, as the more important issues in the application area of outsourcing. Among the merits of outsourcing, both of them considered cost reduction and IS flexibility as the most important factors, However, they chose the difficulty of management control and the lack of operation knowledge among the demerits of outsourcing, Also, they commonly selected overall IS consulting among the components of outsourcing diffusion. In the question of future outsourcing services, user firms chose the adoption of client/server architecture, while SI firms selected the application of multimedia. These results show that there are some differences of preference between user firms and SI firms. Most of user firms consider the outsourcing to maximize information utilization, while the service suppliers focus on new IT adoption and its application to organization. For the strategic use of outsourcing services, SI firms are required to establish the diffusion strategy to meet the outsourcing needs of user firms.