Malagasy primates of the genus Hapalemur are exceptional in their exhibition of specialisations allowing for a folivorous diet despite their small body size. Members of this group are well known for their preference for specific parts of woody bamboo, the primary food resource throughout much of their range. The southern gentle lemur (H. meridionalis), however, inhabits littoral forests that contain little or no woody bamboo. Similar to its closely related congener, the Alaotran gentle lemur (H. alaotrensis), the question is raised as to how these lemurs subsist in this ecological context. The aim of this study was to gain an initial understanding of the ecological niche of the southern gentle lemur in the threatened ecosystem of the littoral forest of southeastern Madagascar. Lemurs were habituated and observed over a 3-month period during the austral winter, allowing for collection of both continuous and instantaneous focal data on their feeding ecology. Preferred food species were identified and collected, and biochemical analyses determined macronutrient and secondary compound values for consumed food items. The diet of the southern gentle lemur was found to be of low nutritional quality, as evaluated through the low protein-to-fibre ratio, especially when compared with other folivores. This lemur is also unique in spending a majority of its time grazing on terrestrial grasses (family Poaceae) during the resource-poor winter months. Our data indicate that Hapalemur spp. possess a behavioural flexibility, and possibly, digestive abilities, higher than previously thought for an animal of its small body size.