Bamboo is one of the main foods of black-and-white snub-nosed monkey (Rhinopithecus bieti). This study is designed to reveal principal chemical components of two bamboo leaves (Fargesia edulis and Fargesia dura), which influence their choice. We collected twenty-one samples of bamboos used by Rhinopithecus bieti at Mt. Lasha, Yunnan from March 2011 to February in 2012. The chemical composition (crude protein, ether extract, total sugar, crude fiber, ash, calcium and total phosphorus) of bamboo were determined from these samples. The results showed that choice of bamboo was mainly affected by higher percentage of calcium and gross energy, and lower ratio of calcium to phosphorus. Thus, the bamboo provides mineral elements required for the survival and reproduction of the monkeys, and is also an important food source of energy. Although there are no differences in the chemical compositions of the two kinds of bamboos, the main factors affecting their choice is different. This may be related to seasonal changes in their chemical compositions. Based on this and previous studies, Rhinopithecus biet prioritizes intake of phosphorus, calcium, and gross energy if macronutrients requirements for protein, ether extract, and others can be satisfied. Main food resources such as bamboo should be protected in the monkey's native habitat since it may be the preferred species of food resource recovery in its destroyed habitats in future.