Dens play an important role in the survival of cavernicolous animals. To explore the characteristics and ecological significance of Himalayan marmot (Marmota himalayana) dens, we surveyed the dens of 30 breeding pairs of Himalayan marmots at Duoma Village, Zoige County, Aba Prefecture, Sichuan Province from May to September 2017 and April to May 2018. Ninety dens that were extensively used (sleeping dens and breeding dens) and temporarily used (temporary dens) were selected, and seven physical characteristics of each den were measured to analyze the differences between those types of dens. We found that the average outer diameter of the den long axis is 59.3 ± 21.9 (16-100) cm, and its mean minor axis is 45.8 ± 20.5 (18-100) cm; the average inner diameter of the den is 24.4 ± 4.0 (16-39) cm, and the average inner vertical diameter is 19.7 ± 3.5 (15-39) cm; the average length is 127.3 ± 43.3 (60-240) cm from the ground to the deepest point of the first tunnel; the average angle of the tunnel is 45.7°± 9.5° (20°-72°); the average entrance orientation is 195.8° ± 96.2° (3°-356°). There are no significant differences in physical parameters of different den types except for the inner vertical diameter between sleeping dens and temporary dens that breeding pairs utilized. The physical parameters of the dens used by the Himalayan marmot indicate that they help to avoid natural enemies, resist bad weather conditions, facilitate water drainage, and maintain the stability of microclimate. The physical characteristics of most of the caves are basically the same by combining behavioral observations, illustrate that Himalayan marmot will change their dens in different years.