Paleozoic and Cenozoic leucogranites are commonly distributed in the Himalayan orogenic belt, and their genesis and geochemical compositions are closely related to various tectonic settings. Boku two- mica granite pluton is located in the western Zhongba terrane. LA- ICPMS analysis on zircon grains yielded an average U- Pb age of 433. 4±2. 0Ma (n=17) with a range of εHf(t) values from -11. 18 to -8. 75. Boku leucogranites show relativelyhigh contents of SiO2(72. 38%~73. 10%), Al2O3(15. 14%~15. 38%), CaO(1. 54%~1. 77%), Sr(141×10-6~174×10-6) and Ba(386×10-6~574×10-6), high ratios of A/CNK(1. 64~1. 77), slightly high δEu values with an average of 0. 80, but low ratios of K2O/Na2O (0. 87~1. 11) and Rb/Sr (0. 86~1. 09). They have a trend of nearly constant Rb/Sr ratios despite large variations in Ba concentrations. All these geochemical features indicate that the Boku two- mica leucogranite is peraluminous- type granite and derived from fluid- fluxed partial melting muscovite in metasedimentary sources, they probably formed in an extensional setting due to slab delamination and asthenospheric upwelling. Different from the contemporaneous Gyirong leucogranites in Tethyan Himalaya derived from dehydration partial melting, they formed in different physical and chemical condition, indicting that the Zhongba terrane and Tethyan Himalaya terrane may have been in different tectonic environments during the Early Silurian.