The Dongmozhazhua Pb-Zn ore deposit in Yushu area of Qinghai Province is one of the important ore deposits located in the "Sanjiang" sediment-hosted base metal ore belt. In the ore deposit, several types of altera-tion and hydrothermal minerals were recognized in previous studies. However, the spatial distribution of the alterations, the characteristics of element content in the minerals, and the spatial and temporal relationships of different minerals in the orefield remain ambiguous, thus the data available couldn't provide clear ore-searching direction. In view of such a situation, the authors made systematic thin section observations of ore and host rocks, systematic electron-probe micro-analysis (EPMA) of the most important sulfides pyrite and sphalerite, and ICP-MS analysis of important metallic compositions of typical ore rocks, with the purpose of finding detailed scientific information on the above problems. Four hydrothermal alteration types were recognized in the ore deposit, namely dolomitization, pyritization, silicification and baritization. Dolomitization is almost distributed in the whole orefield and occurred from S1 to S4 ore-forming stages, whereas pyritization occurred from S3 to S4 ore-forming stages; in both alterations considerable lead and zinc minerals precipitated, and the pyritization was closely accompanied by Pb-Zn mineralization. Silicification occurred in the same time with pyritization and is mainly distributed to the south of the main thrust fault in the ore deposit. Barite precipitated before and after S3 polymetallic sulfide ore-forming stage, and baritization is mainly developed along the faults south of the main thrust fault. Relatively high content of Cd was observed from the typical ore rocks by ICP-MS. According to EPMA, during S3 ore-forming stage, S and Fe content and atomic ratios of S/Fe in pyrite were higher than their theoretical values, some As and Cu were observed, and the ratio of Co/Ni was usually higher than 1; in sphalerite the S content and the atomic ratios of S/Zn were higher than their theoretical values while the Zn content was lower than their theoretical values, and some Cd and Fe were observed. The atomic ratios of S/Fe and S/Zn in pyrite and sphalerite crystallized from most active hydrothermal fluids were obviously higher than their theoretical values; Micro-sections were studied for spherical pyrite and strawberry and crustal sphalerite in this ore-forming stage and some changes of As, Fe, S and atomic ratios of S/Fe in pyrite and Cd, S and Zn content and S/Zn atomic ratios in sphalerite were observed. During S4 ore-forming stage, the sphalerite had similar element content to that in S3 ore-forming stage, but it had lighter color, lower Zn content and higher atomic ratios of S/Zn. Combining the petrographic characteristics and the EPMA results of pyrite and sphalerite, the authors have reached three conclusions: ① in the S3 ore-forming stage, relative to metal ions, S was enough for sulfide crystallization, and the hydrothermal environment was stable in the early time of this stage;with the precipitation of sphalerite, however, the temperature and activity of S and Ph of the ore-forming fluid decreased while the Cd/Zn ratio rose; ② there were two active centers of hydrothermal fluids in the above ore-forming stage, which were located near Line 0 in the MI ore belt and in the north of MIV belt, respectively; ③ the properties of fluids at S3 and S4 ore-forming stages were different, and the latter stage was characterized by lower temperature and higher sulfur fugacity. Based on all these data, the authors give detailed suggestions on the prospecting for similar Pb-Zn mineralization: ① searching for dolomitization and silicification regionally; ② searching for pyritization in the dolomitization and silicification areas; ③ searching for sphalerite and galena at the positions with most pyrite; ④ searching for small-size but high-grade Pb-Zn ore bodies in the baritization areas along faults, and ⑤ searching for Zn-Pb mineralization in limestones with high content of Cd. Four Pb-Zn mineralization locations worthy of detailed work for further prospecting in the Dongmozhazhua Pb-Zn ore deposit are delineated.