This paper intents to suggest the re-engineering methodology to transform and integrate the legacy systems to new system in modern environment. While existing reverse engineering and re-engineering approaches have focused on analyzing and maintaining the source code of program. our methodology can provide the procedures and techniques for evolving into new system by recovering the reverse engineering informations and transforming them into component informations. Our methodology for componentization of legacy system is consisted of plan step, reverse engineering step, componentization step, and delivery step, and we describes activities and detail procedures about each step.