Vegetation is one of the determining factors for soil temperature variation and thermal transfer, which are important processes for the energy and water exchange on the land-atmosphere interface. This study was to understand the impacts of vegetation on soil thermal diffusivity through comparing observations on forested and bared lands. The observations were made in broadleaved Korean pine forest over Changbai Mountain during 2007. The annual cycle of soil temperature and thermal properties at five depths were measured, together with soil volumetric water content and leaf area index.. The soil thermal diffusivity and damping depth of the soil temperature fluctuations were estimated using the heat conduction equation and the sinusoidal-fluctuating temperature at the ground surface. The potential environmental factors for the thermal properties were explored. The results show that soil temperature in both bared land and forest had similar spatial and temporal variations but with different magnitudes. With increasing soil depth, the amplitude of annual temperature variation decreased gradually, while both its phase and annual average temperature itself increased. In comparison with the based soil, the annual average temperature of the surface soil layer in the forest was 0.8℃ lower, the annual amplitude of soil temperature was 2.6-2.9℃ lower, and the temperature phase was 0.2-0.24 rad lower, suggesting that the maximum and minimum temperatures of the forest lagged by 11-14 days behind those of the bare land. The damping depth and thermal diffusivity increased with the soil depth, with an exception for the 1.6-3.2m layers where slightly decrease with depth was observed. It is indicated that soil moisture and leaf area index are probably responsible for the different characteristics in soil temperature and thermal properties between the forest and bared land.