Abstract：The Longshang tin-polymetallic deposit, located in the Xitian area, eastern Hunan, is a large one of the Xitian tin orefield. Its orebodies occur in the contact zones between the Xintian composite granite and carbonate rocks of the Middle Devonian Qiziqiao Formation. In this study, 40Ar/39Ar isotopic dating of muscovite was carried out in order to determine accurately the mineralization age of the deposit. The results show that the 40Ar/39Ar plateau ages of two muscovite samples from the deposit are 155.6±1.3 Ma and 157.2±1.4 Ma respectively and their isochron ages are 155.4±1.7 Ma (MSWD=0.74) and 156.5±1.7 Ma (MSWD=1.4) respectively, which agree within the error limits with mineralization age (150 Ma) of the Heshuxia tin-polymetallic deposit reported previously in the same ore field and are also in accordance with the early intrusive stage of the Xitian composite granite (151-165 Ma). Based on these age data, this paper suggests that the mineralization age of the tin-polymetallic deposit in the Xitian ore field is 150-160 Ma and that their mineralization is closely related to the Xitian composite granite. Both are products during a peak stage of large-scale rock- and ore-forming processes in the early Yanshanian in South China.