As a result of the restructuring of the Korean Power Generation Industry, Korean power companies are under increased pressure to increase capacity and lower operating costs. In order to achieve these goals, an on-line real-time performance monitoring system has been introduced to the Seoincheon and Sinincheon combined cycle power plants (CCPP). The on-line real-time performance monitoring and optimization system helps plant personnel operate the plants profitably by tracking plant performance changes based on real-time information. This paper outlines how the on-line performance monitoring system is being used to improve the operational efficiency and optimize equipment maintenance. Case studies showing the benefits provided by the system are presented. This system will be useful for the plants to respond to the competitive electricity market. (c) 2005 Elsevier Ltd. All rights reserved.