Thermal conductivity of soil samples were measured using a twin transient-state cylindrical-probe method. The system of measurement consists of DC power supply, data logger, personal computer, 100cc soil sample, reference material sample, and two heat probes. The typical results were as follows: (1) Thermal conductivity of soils increased according to an increase of soil water content. (2) The thermal conductivity of Toyoura sand was larger than one of Kuroboku soil. (3) The thermal conductivity estimated by de Vries model had good agreement with the measured value
