Coupled water and heat flow in a grass field was measured using thermo-time domain reflectometry (thermo-TDR) probes during freezing periods. The experimental field, covered with a volcanic ash soil (Andisol), was located in the northern part of Japan with the lowest air temperature of about – 15^oC. The freezing-soil experiment was conducted with an iron-plate placed at the soil surface to produce the freezing condition in the field. Water content and matric potential in soil were measured with the thermo-TDR probes and thermally insulated tensiometers, respectively. The thermo-TDR probes also measured thermal properties in addition to water content. As the soil froze, water content in soil located at a few cm below the frozen soil gradually decreased about 10%. Matric potential decreased as did water content. Since the water flow may be expressed as a function of soil temperature, we suggested a modified relationship between water content and soil temperature for unsaturated conditions. Heat transport occurred from unfrozen to frozen soils. A transition layer between frozen and unfrozen soils might greatly enhance to simulate the heat transport in frozen soil.