In this paper, the effect of surface area of soil particles on the permeability of soil has been reported. The author introduced the surface area of soil particles in order to evaluate the effect of interface phenomenon between soil particle and water (in soil-water system). Discussion on the capi llarytheory and the hydraulic radius theory dealing with the permeability of soil was made on the basis of experimental results. The permeability was measured by the consolidation test, and the

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... of soil particles by the B. E. T. method. The results obtained are as follows : 1) The coefficient of permeability (K) decreased with increase of the specific surface of soil bed (Sv) and it was clarified that the increase of the specific surface of soil bed acts as an increase of the resistance to the water flow in soil. 2) The coefficient of permeability was in direct proportion to the square of hydraulic radius (m) or the product of the porosity (p) and the square of hydraulic radius, which showed. the availability of the theory of hydraulic radius for the permeability of soil. 3) The coefficient of permeability decreased with increase of the number of capillary tubes (n) and with decrease of the radius of capillary tube (r), thereby it became possible to evaluate the per meabilityof soil on the basis of the capillary theory. As mentioned above, it was proved that the utilization of surface area of soil particles is useful for the analysis of the permeability of soil.