OBJECTIVE: To study the material composition of Tibetan medicine "Brag-zhun", and to provide the basis for interpretation of its source and reference for the establishment of quality standards.METHODS: Pharmacognosy routine method was used in macroscopic and microscopic identifications, inductively coupled plasma spectrometry was carried out to determine 26 kinds of mineral elements,and X-ray diffraction analysis was used for the crystalline phase detection of Brag-zhun. The content of calcium,organic matter, humic acid and fulvic acid was determined according to GB/T 14610-2008, "technical specification for soil analysis" , GB/T 11957-2001 and capacity titration, respectively. Moisture, ash content, acid insoluble ash content and water soluble extract were determined with reference to the Chinese Pharmacopoeia (2010 edition). RESULTS: Animal feces were commonly found in Brag-zhun, the main crystal phase was SiO2, 26 kinds of mineral elements content in total was about 3%, 13 batches of medicinal materials in organic matter content was 29.03%-71.79%. Humic acid content was 28.37%-58.51%; fulvic acid content was 19.69%-41.43%; moisture was 5.2% -11.7%; total ash content was 17.82%-64.39%; acid insoluble ash content was 2.10%-39.09%; and water soluble extract was 28.39%-57.40%. CONCLUSION: The traditional record of Brag-zhun from molten juice is lack of scientific basis. The mineral elements in Brag-zhun exist in amorphous. Brag-zhun contains a lot of organic matter including humic acid and fulvic acid, and inorganic matter mainly comes from sediment. The organic matter in rock has gone through a long geological evolution.