The Hetian nephrite belt is the longest nephrite belt in the world with the length of 1 300 km. Besides traditional white, green and black nephrite, a type of brown nephrite was found recently in Pishan County, Hetian, Xinjiang. The nephrite orebody was found in the skarn between dolomitic marble of the Changchengian system and Late Hercynian granodiorite as a metasomatic contact. Under microscope, it is found that the type of brown nephrite is predominantly composed of fibrous tremolite mineral assemblage with minor associated minerals. Brown colors in nephrite have disseminated structure, are distributed in fissures, and occur in forms of disseminations, veinlets or leaves. EMPA, XRD results suggest that the brown nephrite is composed of tremolite together with illite, Mg-olivine, diopside, chromite and some other associated minerals. Fine-grained tremolite crystals in nephrite formed through metosomatism with dolomitic marble and the replacement of diopside by tremolite. Whole-rock chemical analyses of nephrite indicate that chemical compositions of nephrite are similar to those of tremolite. Their bulk-rock REE patterns exhibit strong negative Eu anomalies (δEu=0.09~0.28) with declined LREE, flat HREE and low REE concentration, similar to features of host dolomitic marble samples with negative Eu anomalies, declined LREE, flat HREE and lower REE concentration, indicating a close genetic relationship between them. Test data of the stable isotopes of the ore-forming fluids acquired at 330℃ show that the H and O isotopic values (-81.0‰~-84.0‰ and 3.16‰~5.48‰, respectively) of brown nephrite from the brown nephrite deposit fall in the value ranges of existing marble-type nephrite, but are remarkably different from values of other serpentine-type nephrite deposits, as evidenced by a comparison with other types of nephrite deposits in the world. Also, the ore-forming fluids indicate that it is composed of magmatic water, meteoric water and CO₂ decarbonated from dolomitic marble. Although inverse isochron of phlogopite by Ar-Ar dating suggests that the nephrite formed in 285.23±1.57 Ma, the SHRIMP U-Pb dating of zircons found in nephrite suggest that they formed in 456±7 Ma, which implies that nephrite formed later than this age.