Objective  To explore the body composition characteristics of four ethnic groups in Western Mongolia.   Methods  Bioelectrical impedance analysis was used on the Western Mongolia four ethnic groups 18 indices of body composition. which include Qinghai Khoshut tribe(166 males, 195 females), Xinjiang Chahar tribe (217 males, 226 females), Xinjiang Torgouts tribe(112 males, 127 females), Alxa Khoshut tribe (89 males, 144 females).Using principal component analysis method  to explore the characteristics of the Mongolian body composition in the west of China.   Results  The body composition data of four ethnic groups were obtained. The gender difference of most indicators was statistically significant. The fat rate of female trunk and limbs was higher, while the muscle mass of male was larger. Principal component analysis showed that compared with the southern ethnic group, the northern ethnic group had larger bone mass, more developed muscles and higher level of fat development. On the principal component scatter plot, the distance between the mongols in Western China and other ethnic groups was relatively far, indicating that the body composition of the mongols in Western China had unique characteristics.   Conclusion  Among the Chinese ethnic groups, the Western Mongolians have large bone mass, well developed muscles and high body fat.