In a snowy cold region, it is important to investigate water flow that can be drastically changed by freezing and snow melting during winter. The purpose of this research is to interpret variations of water flow by measuring water contents and matric potential in the grassfield during freezing and thawing periods. The experimental field, covered with the 30�|40 cm thick layer of volcanic ash soil (Andisol), was located in the northern part of Japan, a snowy cold region. The lowest air temperature is about -20oC, and the maximum depth of snow accumulation is about 80 cm in winter. Water content was measeured with time domain reflectometry (TDR), and matric potential under snow accumulation was measured with tensiometry using a pressure transducer, which was protected by thermal insulating materials. Freezing and thawing events were determined by a snow accumulation depth, and soil and air temperatures. At the beginning of winter, water content gradually decreased about 10% as soil was frozen because of free water drainage from the soil surface layer (5�|30 cm). Matric potential decreased as did water content. However, matric potential at 5 cm deep changed from -70 cm to -450 cm accompanied with changes in soil surface temperature from 0.5 to -3oC. This phenomenon might be attributed to water moving upward from the 5 cm depth to grow the frozen soil near the soil surface. It was also found that water condition at a few centimeters below the frozen soil layer seemed soil under dry conditions. On the other hand, as snow melted, the soil surface layer was almost saturated. Especially, matric potential at 45 cm deep reached hydrostatic pressure immediately after snow melting events.