Trypanosoma evansi affects a wide range of domestic animal hosts and can be mechanically cross-transmitted by biting flies when various animals graze together. A total of 1,058 animals (camels, yaks, goats, sheep, cattle, and horses), herded together in the Bayan-Ulgii and Khovd provinces of Mongolia, were screened for animal trypanosomosis using KIN (ITS1) PCR; 21.27% of the samples tested positive. There were significant differences in prevalence among animal species (small ruminants, p < 0.01), sex (males, p < 0.05), and age (adult, p < 0.05). Considering the location, a significant difference in sheep was observed, with the prevalence of trypanosomosis being higher among sheep in Khovd Province (p < 0.01) than in Bayan-Ulgii. This is the first study to highlight the prevalence of animal trypanosomosis in domestic animals that range together in Mongolian grasslands. This study also highlights the significance of small ruminants as possible reservoirs of trypanosomes, and shows the relationship between herd structure, age, and sex and trypanosomosis prevalence in Mongolia.