Abstract: In order to determine the Late Cretaceous tectonomagmatic activities and the significance of granite mineralization in the Tengchong Block, this study applied the comprehensive methods of geochronology, Sr−Nd−Pb isotopic and whole−rock geochemical analyses to probe Xiaolonghe granites. The results show that the Xiaolonghe pluton is composed of fine−grained leuco−monzogranite and porphyritic−like biotite monzogranite. Zircon U−Pb chronological data indicate that their magmatic crystallization ages are 67.0±1.0 Ma and 68.5±1.6 Ma respectively, and the Re−Os model ages of molybdenite are 67.15±0.99 Ma and 69.02±1.22 Ma respectively, both of which are the products of the Late Cretaceous tectonomagmatic activities. The characteristics of Sr−Nd−Pb isotopes and major and trace elements show that the fine−grained leuco−monzogranite is S−type granite ((⁸⁷Sr/⁸⁶Sr)_i=0.757 ~ 0.763, ε_Nd(t)=−8.89 ~ −8.99), and the magma originated from the partial melting of clay−rich hard sandstone in the upper crust of Mesoproterozoic(T_DM2=1.59 ~ 1.60 Ga), which is closely−related to the formation of Xiaolonghe tin−tungsten polymetallic deposit. The porphyritic−like biotite monzogranite is I−type granite ((⁸⁷Sr/⁸⁶Sr)_i=0.711, ε_Nd(t)=−8.72 ~ −9.16), and the magma originated from the remelting of clay−rich hard sandstone in the lower crust of Mesoproterozoic(T_DM2=1.58 ~ 1.62 Ga). The Late Cretaceous Xiaolonghe granites and its tin−tungsten mineralization in the Tengchong Block are the products of magmatic activity and hydrothermal process caused by the collision or post−collision between the Tengchong Block and the Baoshan Block after the closure of the Meso−Tethys Bangong−Nujiang ocean.