In southwestern Taiwan, a land of over 1000 km^2 is covered by the geological formations consist of mainly mudstone or shale. The slopes in this region have a lot of natural hazards which are related to their geological characteristics. Among these geological formations, Nanhua Mudstone is the worst one for geological hazard, especially for erosion problems.This paper summarizes the previous study about the engineering geological characteristics of the mudstones (shales) in southwestern Taiwan. Most of the geomaterial are related to Nanhua Mudstone. It also postulates the major causes of the erosion problem of Nanhua Mudstone. Finally, several hazard mitigation methods are suggested.