This study proposed the procedure of mountain slope partition for landslide hazard assessments focusing on a hierarchy of slope units. The objective of this study was to partition slope units using DEMs with different spatial resolution by comparing the results in the Akaishi Mountains and the Shikoku Mountains, Japan. We used three type DEMs with a spatial resolution of ca. 50 m, 30 m, and 10m grid-cell. In general, individual slope units are partitioned by drainage and divide lines. We therefore newly defined an order of divide lines and partitioned slope units. Divide lines were regarded as catchment boundaries. An order of divide lines was defined according to frequency of divide lines that were extracted as catchment boundaries from DEMs, with changing area conditions of catchment identifications. By partitioning slope units with these divide and drainage lines, slope units therefore had relative hierarchy corresponding to the order of divide lines. These procedures were validated and cross-checked using both different spatial resolution DEMs and the different study areas, considering the relation between slope angle and relative height of each unit. Partitioned slope unit maps indicated that there were inclusive relations among the hierarchies; i.e., a slope unit consisted of units with a low-order one, and was included in a high-order one. Scatter diagram of slope angle and relative height of each slope unit showed a concentrate distribution. These results were confirmed in both different DEMs and the study areas.