Located in the East Qinling molybdenum belt of Shaanxi Province, the Shijiawan ore deposit is a large porphyry deposit. Mineralization of the deposit consists of quartz-molybdenite veinlets and stockworks which occur in altered granite porphyry and wall rocks. Hydrothermal alteration is composed of potash feldspathization, silicification and sericitization. Direct Re-Os dating of molybdenites collected from different ores in the Shijiawan deposit was carried out to better understand the age of mineralization. The results show that molybdenite samples yield ¹⁸⁷Re-¹⁸⁷Os model ages ranging from 143.1±2.1 Ma to 145.1±2.2 Ma, with the average of 144.0±1.1 Ma (MSWD=0.91), and give an isochron age of 145.4±2.1 Ma (MSWD=0.83). These ages are close to the zircon U-Pb ages of Shijiawan feldspar-granite porphyry (141.4±0.6 Ma), indicating that mineralization occurred in Late Jurassic-Early Cretaceous period. In combination with the evidence from S isotope, Re content and chemical characteristics of the related pluton, the authors hold that the ore-forming materials were mainly derived from the crust, with the addition of a little mantle material.