The purpose of this study is to improve of energy performance in school buildings. Many building renovations have mainly focused on commercial buildings and houses, but school buildings have no attention in this field although there are many buildings that show degraded energy performance and there are many old fashioned buildings which need renovation. This study was carried out through the survey, field study, energy simulation and life cycle cost analysis. The results of this study can be summarized as follows: In model building, large amount of heat were lost at the building envelope, such as non-insulated skins, window-sills and window-frame joints. According to the simulation result, about 15％ of heating energy is saved by the insulating works compared to pre-renovation condition. Also, LCC analysis revealed to be more effective to select a exteria wall insulation such as a dryvit system.