Soils of the slope on the southern side of the Sansyou-uo swamp in the Institute for Nature Study were surveyed. Parent material and horizon differantiations of 4 pedons on the slope were investigated. Hydro-condition was estimated from the value of moisture weight/maximum water capacity. Hydro-condition of pedon corresponded with the relief as described below. Pedon A was located on the foot of the slope, and the hydro-condition was moderately moist. Pedon B and C were located on the side of the slope, and weakly dried. But the microrelief of pedon C was flat. Pedon D was located on the top of the slope, and dried. It is also proved that these soils were derived from volcanic ash. It is obvious that there were high degree of human impact for many years on these soils from the historic document. These soils were classified as Andosols, and it is also known that soil profile development of these soils took more than hundred years, and formed mainly under the grass vegetation. So it is doubtful whether mineral horizon of these soils were developed under the present condition of vegetation of forest. Horizon differantiation of mineral horizon of these pedon did not necessarily correspond with the hydro-condition. Horizon differantiation of organic horizon (Ao horizon) of these pedons corresponded to the hydro-condition. Ao horizon of pedon A was thin, and mull type. Ao horizon became thicker corresponding with the hydro-condition and changed to moder type. Pedon D was found to have thicker Ao, and mor type. It is concluded that the soils of the slope on southern side of the Sansyou-uo swamp were the hydro-catena, of which Ao horizon corresponded to the hydro-condition caused by the relief.