application/pdf Using a hand-made thermal probe, measurements were made by a non-stationary absolute method as to the dependence on temperature of thermal conductivity of frozen soil by changing temperature in a range from 20 to -170℃ and keeping as invariable as possible such other factors as moisture content, particle size distribution, mineral composition, dry density, etc. Soil samples were prepared from volcanic ashes, which were sieved so that they comprised particles of 0.105 to 0.250 mm in diameter. The moisture content of each sample was arranged from 0 to 60 percent by adding a corresponding amount of water to oven-dried soil, so every sample had the same dry density. It was revealed that the following three formulas are in a good agreement with the results of the experiment. (i) Thermal conductivity of frozen soil varies with temperature in the following relation : K=A･T^B (A and B are constants ; T is the absolute temperature.) (ii) Thermal conductivity and moisture content have the following relation : K=C･e^ (C and D are constants : w is the moisture content.) (iii) The value of thermal conductivity K_G calculated from the geometric mean by the following formula agrees well with the value of observed thermal conductivity K: K_G ＝Ｋ^φ_ss･Ｋ^φ_aa･K^φ_ww・K^φ_ii, where K_s, K_a, K_w, K_i, express thermal conductivity for soil particle, air, water and ice respectively ; φ_s, φ_a, φ_w, φ_i express volumetric ratio of each component in the same order.