In this paper, the authors present the main results of the long-term monitoring of permafrost in Mongolia. In Mongolia, permafrost is degrading at different rates under the influence of climate warming. Average trends of the increases in active layer thickness and mean annual ground temperature are 5-20 cm and 0.1-0.3°C per decade, respectively. These trends of the last 15-20 years are higher than those of the previous 15-20 years. Furthermore, the degradation of permafrost in Hövsgöl mountainous region is more intense than in the Hentei and Hangai mountainous regions. Since permafrost plays an important role in the maintenance of ecosystem, the recent degradation of permafrost may lead to significant changes in ecosystem, especially in soil thermal state and moisture content.