In Mujoo area, the granitic pegmatites are developed in the granitic gneiss complex with Jurassic gneissic granites, where Nb-Ta mineralization were reported. Pegmatites are mainly composed of large crystals of quartz, feldspars of end-member orthoclase and albite, and muscovite. Nb-Ta minerals in study area are columbite (Nb > Ta) in composition. Chemistry of muscovites shows post-magmatic in origin and they are closely related with columbite. Large columbite, in pegmatites occurred with quartz and feldspars, while microcrystalline columbite is associated with muscovite. The Nb contents in large columbite are relatively higher than those in microcrystalline ones. Two pegmatites, 4~15 m in width and 120 m, 250 m in extension respective1y, are developed. Five drilling cores with total 600 m in length are finally obtained and revealed no possible potential for economic rare metals of Na-Ta deposits.