To preserve competitiveness in rapidly changing world military market and to adapt themselves to newly-developed warfare, many developed counties have been readjusting their military organizations and technical procedures. In a private sector, business reengineering and other innovative efforts were made to respond to this change, using structural approaches. In the military sector, the United States is the one leading this move. She has been trying to reorganize her military structure to hold her hegemony in world politics for the coming 21st century. The purpose of this paper, is, (1) to analyze the information technology on the military revolution, (2) to deduce what to be changed, and (3) to infer how to change. The comparison between Korea and U.S. in terms of the real military situation was made to analyze these three research questions. The study was based on the structural contingency theory, one of the environmental analysis models, being introduced to explore the Revolution in Military Affairs(RMA) case in United States and Korea. The conclusion may be summarized as follows; First, information-based society which is characterized by the development of information technology and environmental, complexity and weakness in security affairs will affect the military factors such as the issue of holding information superiority, changing warfare in proportion to the military-scientific development and weakness in military security. This trend will be more deep-rooted and multiple in its influence on the military affairs.