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Studies on the ontogenetic shifts in sexual dimorphism in head size (head length and width) and food habits of Eremias brenchleyi were studied. The results showed that adult E. brenchleyi had no obvious sexual dimorphism in body size (SVL). Both sexes differed in head size since hatching, with males having larger heads than females. This sexual dimorphism was much more pronounced between adults than between juveniles (including hatchlings), largely because the increase velocity of head size of males with SVL was faster than that of females. Hatchlings had relatively larger heads to SVL than juveniles and adults, presumably because E. brenchleyi embryos allocated relatively more resources for early survival and growth of hatchlings. Head size of both sexes overall showed an allometric growth pattern with SVL increase ontogeny. Lizards of different sizes and sexes differed, in certain degrees, in food niche breadth and niche overlap. However, no direct evidence showed a noticeable contribution of the divergence in head size to the segregation of food niche between males and females, thereby mitigating the competition between both sexes.