African elephants (Loxodonta africana) are mixed feeders, incorporating varying proportions of grass and browse into their diets. Disagreement persists as to whether elephants preferentially graze or browse, and the degree to which the consumption of these foods is a reflection of their local availability. We used stable carbon isotope analysis of feces to investigate seasonal and spatial variation in the diets of elephants from Kruger National Park (KNP), South Africa. Elephant diets (overall average ∼35% grass) are shown to be distinct from those of grazers (>90% grass), browsers (<5% grass), and another mixed-feeder, the impala (Aepyceros melampus; ∼50% grass). Fecal δ¹³C values suggest that elephant populations from northern KNP eat more grass (∼40%) during the dry season than do their southern counterparts (∼10%). The wet-season diets of elephants from northern and southern KNP include similar amounts of grass (∼50%), because elephants in the south, but not in the north, ate significantly more grass during this time. Although habitat differences in KNP appear to account partially for variations in elephant diets, the specific influence of each habitat type on diet selectivity is not clear. The homogeneity of woody vegetation in the north (dominated by Colophospermum mopane “shrubveld”) may deter browsing and force elephants in this area to opt for alternative food sources (grass) throughout the seasonal cycle.