The impact of increasing numbers of livestock on wild ungulates has been a concern in Mongolia. We used DNA barcoding via next generation sequencing to reveal detailed food habits and assess the extent of potential resource competition among ungulates in the desert steppe of southern Mongolia. From feces of 2 wild (Mongolian gazelle [Procapra gutturosa], Asiatic wild ass [Equus hemionus]) and 4 domestic (sheep [Ovis aries], goat [Capra hircus], horse [Equus caballus], camel [Camelus bactrianus]) ungulates collected in June 2014, we identified 25 plant families (39 to genus and 18 to species). Dietary diversity was the highest for sheep (Levins' standardized index = 0.351), followed by goats (0.342), and the lowest for gazelles (0.220). Gazelles had a high dietary overlap with goats (Pianka's index = 0.654) and sheep (0.630). Wild asses had the highest dietary overlap with horses (0.847), followed by goats (0.727) and sheep (0.719). The high dietary overlaps may be explained by similar digestive systems and body sizes among gazelles, sheep, and goats and between wild asses and horses, and by the high dietary diversity of sheep and goats. The present study shows more diverse food compositions than previous studies, suggesting that because of the high dietary diversity of sheep and goats and their overlap with wild species, their increasing number is a potential risk for the survival of wild ungulates.