Due to recent occurrence of regional heavy rain events, the amount of life loss and property damages is increasing every year. In case of South Korea, it is necessary to have a pretty accurate weather forecasting system to predict regional heavy rain events during rainy season in summer since typhoons or heavy rains result in urban inundation. In this study, we select 12 government districts out of the important districts and metropolitan cities and determine the accuracy of heavy rain forecasts by comparing the observed rainfall data and heavy rain forecast announced by KMA based on the old and current two criteria for issuing heavy rain forecast which were revised in June of 2011. Also, by comparing the regional design rainfall for each return period and heavy rain warning, it may contribute to improve the accuracy of heavy rain forecast and suggest a way of the application for each region.