The manner in which animals use potential food in their environment, the diversity of species they consume, and the seasonal variation they display in their preferences for food, forms the basis of adaptive foraging strategies that maximized fitness. Although food specialists are more sensitive to environmental change than are food generalists, all species must meet their nutritional requirements while avoiding the potential harm that can result from the ingestion of noxious materials. François' langur is a rare and threatened primate that is endemic to the limestone habitat of southwest China and northern Vietnam. In recent decades, the langur population has declined rapidly, and remnant populations are severely threatened by habitat fragmentation. Elucidating the spatial and temporal foraging habits of langurs will provide an understanding of the mechanisms by which langurs respond to habitat fragmentation and allow us to speculate on the adaptive significance of these strategies. In this study, we investigated the dietary diversity and seasonal variation (i.e. the monthly overlap in species consumed) of François' langurs in a fragmented forest habitat in Fusui County, Guangxi, China. Field observations were obtained via focal animal sampling. These were conducted for eight days at the start of each month throughout 2006. On each day of sampling we randomly selected a focal adult and observed that individual from 06:30 until 19:30. This observation period was divided into 15-min sessions, with foraging behaviors (i.e. the species of food consumed and the time spent feeding) recorded only during the first 5 min of each 15-min session. Analyses were conducted to determine the monthly dietary diversity and the degree of temporal (monthly) overlap in dietary species. We found that the annual dietary diversity of langurs at this site was 3.03, with the lowest diversity recorded in January (1.93) and highest diversity recorded in December (2.62). There was no significant monthly variation in the dietary diversity index (One-sample K-S Test, Z = 0.44, n = 12, P = 0.99), which suggests that langurs exhibit little variation in the number and types of species they consume throughout the year. Nevertheless, some species (for example, Pteroceltis tatarinowii and Litsea glutinosa) were consumed in all months, whilst others were consumed more selectively, in some months but not others, despite being available in all months. The degree of monthly overlap in species consumed ranged from 0.75 (September and October) to 0.42 (March and April). Our results suggest that the foraging strategy of langurs in fragmented habitats could be characterized as being generalist as a diverse number of species were consumed throughout the year. This strategy is likely to be adaptive in this fragmented habitat, because langurs must balance the need to consume food efficiently, so as to meet their nutritional requirement, with the need to selective in their preferences, so as to avoid consuming plant species that contain noxious secondary compounds. Our work has shown that langurs maximize their foraging efficiency by foraging predominately on common species that are readily available in the environment, and subsequently, supplementing their diet with rare plant species that are of high nutritional quality. We contend that this foraging strategy maximizes the langurs' survival probability and reproductive success in fragmented habitat.