In most mountainous parts of the temperate zone of Japan along the Pacific Ocean, some climatic climax forests, whose main dominant species is Fagus crenate, F. japonica or Quercus mongolica var. grosseserrata, are distributed. In the riparian regions of the zone, however, there appear summer green forests composed of the different species from the climatic climax forests. Climate plays an important role in determining the overall distribution of vegetation, but some environmental factors, i.e., topography, soil type, soil moisture content, etc. have a great influence on vegetation formation. Riparian forests seem to be controlled by various geomorphologic disturbances, such as landslide, soil erosion and accumulation. The study aims to present the relationships among vegetation, soils and landforms in the process of determining riparian forests dominated by Fraxinus platypoda and Pterocarya rhoifolia establishment in the mountainous region of central Japan. The study area extends an area of 302 ha with a range of elevation between 925 m and 1,681 m at the Chichibu mountains. The landforms were corditied at sampling grids (25 $ imes$ 25 m, n = 4,843) using a hierarchical system, and a brief description of the forest soil classification was also given. The mutual relationship analysis indicated that forest soils and landforms play a significant role in determining the geomorphological process of riparian forest, and shaping the ultimate pattern of vegetation. At the study area, riparian forests were mainly found on the $B_E$ forest soil type and steep slopes ( > 30$^{circ}$) at convex slopes along the streams. On the other hand, the direction of slopes did not have a significant impact on the establishment of the riparian forests. A mosaic of patchy distribution of those riparian forests on the slightly wetter $B_E$ forest soil type was one of the characteristic features of the study area. This particular soil which contained large talus gravels was found on the land formed by erosion and deposition of landslide.