Soils of pedon A, B, and D on the slope on the southern side of the Sansyou-uo swamp in the Institute for Nature Study were the hydro-catena, of which Ao horizon differantiation corresponded to the hydro-condition caused by the relief. Soil respiration(SR) of these soils were determined as the criteria of the decomposition of soil organic matter by soil microorganisms, and discussed about the relationship between the hydro-condition and decomposition of soil organic matter. Number and biomass-carbon of the microorganisms, and organic matter and sugar in the water extracts of soils were also determined, and discussed about the relationship between these values and the hydro-condition or decomposition of soil organic matter. Hydro-condition of A was moderately moist, and SR was high. That of B was weakly dry, and SR was middle. That of D was dry, and SR was low. SR was corresponded with hydro-condition. SR became lower by drying treatment of soil, and became higher by wetting treatment. It is considered that SR was influenced mainly by the hydro-condition of soils. It could also be observed the positive relationship between SR and number of the bacteria, or pH of soils. It could be observed that the negative relationship between SR and number of the fungi, or amount of organic-carbon, total sugar in soils and water extracts. It is considered that SR rate caused by mainly hydro-condition influenced the accumulation of soil organic matter in A horizon, and also influenced the depth and the differantiation of Ao horizon.