We examined the dietary diversity and food intake of Phrynocephalus frontalis, compared the difference of insect diversity in the natural habitats with different lizard densities, and discussed the potential role of this lizard in the desert ecosystem. The results show that:(1) arthropodans of the orders Coleoptera, Hymenoptera and Hemiptera were major dietary components of P. frontalis;(2) coleoptera larvae always formed the predominant component of lizard diets;(3) dietary diversities of P. frontalis were not significantly different between summer and autumn or between the two sexes;(4) the similarity in trophic niches between seasons was 0.756, whereas the similarity in trophic niches between sexes was 0.994;(5) stomach content weight of lizards varied signiifcantly among different seasons, but there was no signiifcant difference in stomach content weight between sexes;(6) insect diversity differed signiifcantly among the groups of the habitat with different degrees of lizard density, and the habitat with moderate lizards density had the highest insect diversity. We infer that P. frontalis prey mainly on insects and change their diet and food intake with season;males and females consumed similar preys in types and weights. As an important predator, P. frontalis could affect the insect community in the arid ecosystem of Hunshandak Desert on the Mongolian Plateau.