The diet of wild non-human primates is still largely unknown, but advances in molecular techniques using DNA metabarcoding allow obtaining such information much faster and in more detail than until recently. The genus Trachypithecus is the most speciose and most broadly distributed genus among Asian colobines, a group of highly folivorous primates. The genus contains four species groups of which three occur in rainforest habitats while the fourth, the T. francoisi group, is restricted to limestone habitat. To characterize the food plant composition of langurs living in different habitats, we employed a metabarcoding approach and analyzed monthly samples (n = 419) collected over a 1-year period from T. crepusculus and T. germaini, members of the T. obscurus and T. cristatus groups, respectively, and T. delacouri and T. hatinhensis, both members of the T. francoisi group. By identifying plant taxa primarily to the genus level, we found that langur species consume a large number of different plants, with diets comprising of 122 - 129 plant genera across 59 - 73 families. While both overall dietary diversity and the most common plants consumed differed among the four species, we found no clear distinction between rainforest and limestone langurs. The four langur species also differed in their reaction to seasonal changes, as some species consumed different plants during dry and wet season, whereas others showed little change in plant consumption over the year. This study improves understanding of Trachypithecus dietary composition and represents the first dietary inventory of T. crepusculus in Vietnam.