This study examines the performance of a regional climate model (RCM) for simulation and prediction of a summer monsoon over Korea in 2003. National Centers for Environmental Prediction (NCEP) Regional Spectral Model (RSM) is used. First, a regional climate model is driven by reanalyzed atmospheric forcing was provided by the NCEP-DOE data. In the second phase of a methodology to test a nested modeling system a regional climate model is driven by general circulation model (GCM) ensemble forcing. Finally, we introduce a transfer function to correct the systematic bias of regional climate model. This transfer functions are obtained from the observed precipitation data for 10 years and 10-year simulation data obtained from regional climate model. The preliminary result showed that RSM simulates the large scale feature close to observation with the new physics options. The model was able to capture the monsoonal rain band. However the rainfall simulated by reanalysis-driven RSM appeared to be deficient in Korea. Some sensitivity experiments of simulated monsoon to physics options will be discussed.