Most volcanic ash soils in South Korea are distributed in Jejudo which is an island placed on southern part of Korea and has steep slope mountain area. There are many soils containing high contents of organic matter (OM) made by volcanic ash in Jejudo, also. Therefore, irrigation and drainage etc. in volcanic ash soil have to be applied with different management way compared with general soil which has low OM content, but studies seeking appropriate methods for them are set on insufficient situation because the area of volcanic ash soil in South Korea is only 1.3% (130,000ha). This study was conducted for searching a relation of gravimetric soil water content (GSWC) and organic carbon (SOC) affecting water moving in volcanic ash soil, and 21 soil series among 65 soil series in Jejudo were analyzed for this study. The relation had the form of power function (Y = a∙X^b) by each water tension (10-1500 kPa) like as Fig. 1, where Y is GSWC, X is SOC, and a and b are coefficients. The value of a which is the coefficient of power function showed regular decreasing tendencies, and b showed also regular tendencies so that the equations, which are functions of water tension , expressing the tendency were sought by statistical analysis.