Ningwu Basin, which is characterized by widespread porphyritic iron ore deposits, is one of the seven ore concentration areas in the Middle and Lower Yangtze metallogenic belt. The Washan iron deposit, which is one of the important representatives of porphyric iron-ore deposits in Ningwu Basin, is located in the middle of the basin. In this study, the result of Re-Os isotopic dating of pyrites collected from the Washan iron deposit was reported. It is for the first time that the metallogenic age was determined by iron-bearing metallic minerals in Ningwu area. The results show that the Re-Os isochron age of pyrites in Washan iron deposit is 127.7±2.6 Ma(n=5,MSWD=0.66), which can directly represent the metallogenic age of the Washan iron deposit. The initial ¹⁸⁷Os/ ¹⁸⁸Os ratio is 1.73±0.56,and the γ_Os(t) values are from 527.18 to 535.93, which are between the value of the mantle and that of the crust. Combined with previous studies, it is suggested that ore-forming materials of the Washan iron deposit was mainly derived from the enriched mantle and partly from the crust.