Located in the middle segment of the Three River region, the Yunlong metallogenic belt is considered to be connected with the Southeast Asian giant tin belt. The authors performed LA-ICP-MS zircon U-Pb analysis of two-mica granite closely related to tin mineralization, and got a Late Cretaceous emplacement age of 72.2±0.8 Ma (MSWD=1.9). This is the first discovery of convincible Late Cretaceous magmatism in Baoshan terrane. The two-mica granitiod in Yunlong tin metallogenic belt was emplaced in a tectonic setting identical with the setting of the Tengchong terrane, and could represent the melting products of thickened crust in the hinterland in response to the eastward subduction of the Neo-Tethys. The emplacement age of the two-mica granite reported here is synchronous with an important tin metallogenic period in the Yunlong tin metallogenic belt. These data, combined with previous reports, suggest that the three important metallogenic periods in the belt corresponded respectively to contemporaneous tectonomagmatic events. That is, the Early and Late Cretaceous ones were closely related to granitoid emplacement, whereas the Cenozoic one was related to the strike-slip shearing of the Chongshan shear zone. The genesis of tin deposits in the Yunlong tin metallogenic belt can hardly be explained by one single model (granite-related magmatic-hydrothermal or migmatitic-hydrothermal model). Granitic magmatism and tectonic-related migmatism had both contributed to the formation of tin deposits, but they played different roles in different metallogenic periods.