Economy of scale would be one of the most important issues among organizations pursuing system integration projects. Cerntainly there are other benefits than cost reduction for achieving system integration. However. these benefits could not be achieved automatically. if system integration projects were undertaken without thoughtful planning. In this paper. we propose a framework for an effective system integration by (1) defining the objects(user interface. database. application. and server) and (2) considering the level of integration(physical integration and rational integration). Therefore. 6 types of integration can be considered. Five case studies of domestic organizations were reviewed to suggest various issues and solutions. Based on our case studies. we discovered that five integration types - EIP. EAI. ERP. BPM and System Reconsolidation - were most widely used.