Geophagy, or soil ingestion, is the deliberate act of eating soil. This behavior is a widespread practice in the animal world, particularly among generalist herbivores and primates. Primates consume a wide and complex variety of food items that vary temporally and spatially. Mature leaves, flowers, leaf buds, fruits, seeds and invertebrates constitute the bulk of potential food items. The close link between geophagy and primates suggests a need to ingest soil. Various nonexclusive principal functions have been advanced to explain geophagic behaviors, the main ones being: taste enhancement, detoxification of noxious or unpalatable compounds present in plant foods, supplementation of mineral nutrients, alleviation of gastrointestinal upsets such as diarrhea, counteraction of the effects of endoparasites and reduction of excess acidity in the digestive tract. So far no studies on the possible adaptive significance and ecological consequences of geophagy in primates have been published in China. In this paper we report 207 incidences of geophagy observed among provisioned Thibetana macaques (Macaca thibetana) at Mt. Huangshan, China. The group consisted of 19 animals that were routinely provisioned (four times a day) with cereal corn that supplemented their natural food sources. We gathered data on the identities, ages and sexes of participants as well as the frequency, amounts, duration of geophagy. Soil samples (uneaten and eaten) were analysed for the following chemical and physical properties: soil color, pH, water content, mineral elements. The purpose of the study is to describe the behavior of geophagy and its implications for provisioned species. The results show that soil is sought and purposefully selected, and that some sites are preferred and have been mined by many individuals for a long time. Soils that the monkeys choose are yellow or yellow-brown, weakly acid, with an abundant amount of clay, and are richer in certain mineral elements, especially iron, calcium and magnesium than uneaten soil. Organic-rich soil appears not to be eaten by the monkeys engaging in geophagy. All age groups and both sexes consume soil, but adults as a group are more inclined to geophagy than the other age groups. Mean duration of geophagy does not differ significantly with age or sex. Mean frequencies and amounts of geophagy do not differ significantly by social rank for either males or females. Adult females are the most frequent consumers of soil. Mineral supplementation during pregnancy and lactation may be important as a stimulus to geophagy behavior of adult females. This study supports the food detoxification hypothesis that the soils consumed regularly by Tibetan macaques feeding on a variety of plant species help to absorb the toxic constituents therein. Monkeys showed a decided preference for geophagy especially when they were heavily provisioned. It is possible that Tibetan macaques ingest clay to alleviate gastric upsets made by high energy, low fiber human foods. Tibetan macaques may indulge in geophagy for one or a combination of reasons. Therefore future research requires interdisciplinary efforts among soil, plant and animal sciences, focusing on the roles of geophagy vis a vis primate nutrient requirements, parasitology, feeding ecology, phytochemistry, soil microbiology, mineralogy of soil, and effects on the bioactivity of consumed plants.