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Savannah (C4) grasses are first recorded at low latitudes in the mid-Miocene prior to their expansion towards mid-latitudes by approximately the Miocene-Pliocene boundary. In an attempt to determine the timing of the spread of savannah grasses into the South African highveld, a palaeoecological study of some of the oldest faunal deposits in the region (mid-Pliocene) was undertaken. The combination of carbon isotope and dental microwear analysis of micromammals from the Rodent Corner and the Exit Quarry repositories of the Makapansgat Limeworks has enabled the determination of the relative proportions of C4 grass, C3 grass and C3 browse in the diets of two extinct herbivorous rodent species, Otomys cf. gracilis and Mystromys cf. hausleitneri. M. cf. hausleitneri is shown to have a similar diet to the extant Mystromys albicaudatus whereas O. cf. gracilis is shown to be less reliant on grazing than the extant Otomys irroratus, despite its specialised hypsodont molars. The lack of a grazing specialist amongst the most common species in the Makapansgat micromammal assemblages is suggestive of a local palaeo-environment that was more wooded than the present day woodland-savannah mosaic. The presence of C4 grasses in the mid-Pliocene of Makapansgat indicates that the spread of C4 grasses into the South African highveld occurred prior to this time.