We determined the dietary habits of two sympatric and allotopic populations of Ctenomys (C. australis and C. talarum) that inhabit a natural dune grassland on the sea coast at Necochea, Buenos Aires Province, Argentina. Both species were found to be generalist herbivores as they consumed almost all plant species available in the grassland. Contrary to what we had expected, they fed principally on the aerial fraction of the vegetation, and preferred gasses over forbs. The greater proportion of the subterranean fraction in autumn and winter in C. australis diets compared to C. talarum might be related to differences in the vegetation around the burrows they inhabit. Ctenomys australis and C. talarum diets differed markedly only in September; however, these differences may not have been totally seasonal, there may also have been a spatial effect due to the soil structure of the sympatric area. Ctenomys australis and C. talarum distributions seem to be related to soil characteristics with individual animals feeding and selecting mainly among the vegetal species in their own home range. The results of this study show that these species of Ctenomys present a feeding strategy which is adaptative in subterranean rodents due to their high digging cost and to the low available energy to explore in their subterranean environment.