So far, our study on LIDAR has covered the data collection on pilot areas, accuracy assessment, and error analysis. For obtaining the elevation of bare earth surface from LIDAR data, human interaction consumes some 60-80% of processing time. The report of ISPRS WG-III3 shows that errors due to imperfect of filters are mostly in complex urban areas and rough terrain with vegetation, which is the case in Taiwan. And, the influence of point density could not well be determined in ISPRS experiment. Thus, in this study, data acquired in forest area of mountainous terrain in Taiwan will be processed by selected software with algorithms and parameters assessed for optimal performance.