Comparative studies of nonhuman primate species that utilize different habitats are essential for understanding their behavioral and ecological plasticity. Furthermore, results from such studies can assist in formulating conservation strategies by evaluating a species’ capacity to cope with changes in habitat quality resulting from natural process or human disturbance. We compared dietary profiles for François’ langur (Trachypithecus francoisi) in Nonggang National Nature Reserve, Fusui Nature Reserve, and Mayanghe National Nature Reserve to evaluate inter-site variation in diet. Our results showed that a total of 259 plant species belonging 182 genera from 77 families were consumed by the langurs. Woody plants, including trees and shrubs, were the most important food resources. Langurs were highly folivorous, with leaves accounting for 52.7%, 63.9%, and 79.7% of their diets, respectively. However, we found that diet differed between study sites, with overlaps of 1.33% to 7.43% for total food species, and 0 to 13.51% for main food species. This variation could be related to differences in forest composition. Compared to congeners in Nonggang and Mayanghe, langurs in Fusui ate much more young leaves and shrubs. These differences reflected changes in forest structure resulting from human disturbance. Marked variations in the diets of T. francoisi at different sites suggest dietary flexibility, which could be important for their survival in different habitat conditions.