Karst is a special habitat for most of the nonhuman primate, its forest has some unique features, such as poorer, but more diversity vegetation, and the items of plants used for food by primates showed seasonal fluctuation. The availability of food resources was influenced by environment, according to previous data from other primates inhabited in karst habitat. Franois′ langur (Trachypithecus francoisi) is one of the few primates that inhabit in karst habitat. So, how did the Franois′ langur obtain adequate food according with food availability fluctuation? Did they adopt a common feeding strategy selected by most species living in mountains, or the special one adapted to karst? To explore what feeding strategy the Franois langur would adopt in response to seasonal scarcity of preferred foods (immature leaves, fruits), we investigated the dietary composition and its seasonal variation of one group of the Franois′ langurs at Nonggang National Nature Reserve, Guangxi, China, from September 2005 to August 2006. Data were collected by instantaneous scan sampling. The results indicated that totally, 92species of plants were used for food by langurs, there were 38 species of trees and shrubs, 52 of vines, 1 of herbs, and 1 of Epiphyte. On average, langurs monthly consumed 22.8 plants species, and the food diversity index (FDI) was 2.5. Leaves constituted 71% of the langurs′ diet, including 46.9% immature leaves and 241% mature leaves. Fruits, flowers and seeds contributed to 13.2%, 6.3% and 4.3% of their diet, respectively. Other food items accounted for 5.4% of the diet, including 1.8% stems, 1.1% petioles, 2.5% unidentified parts, respectively. There were significant seasonal variations in langurs′ diet. The total number of food species and the FDI in dry season were both higher than rainy season (Food species: 29.3 vs 16.2; FDI: 2.8 vs 2.1). During the rainy season, when leaves were abundant, their diets consisted primarily of young leaves, which contributed 61.5% in dietary, higher than a proportion of 32.3% in dry season. Consumption of mature leaves and seeds increased significantly in the dry season when young leaves and fruits were scarce, both having a higher proportion than in rainy season (Mature leaves: 39.4% vs 89%; Seed: 86% vs 0%). Our results also demonstrated the influence of food availability on dietary composition. Positive relationship between the proportion of young leaves in monthly dietary composition and their availability in the karst habitat was found（Spearman rank correlation, r=0.865, n=12，P<0.01）.The availability of mature leaves and fruits both decreased when the FDI increased（Mature leaves：r =-0.602, n=12，P=0.039 ；Fruits：r=-0.716, n=12，P=0.009 ）. Similar to most of langur species, Franois’ langur adopted a feeding strategy of more mature leaves and seeds to respond to the dry season of less prefered food, with a higher dietary diversity.