Cenozoic ultrapotassic volcanic rocks have typical lamproite characteristics such as high SiO2, MgO, K2O and TiO2, low Al2O3 and Na2O, and high K2O/Na2O ratios. Geochemical and Sr-Nd-Pb isotopic characteristics of these ultrapotassic volcanic rocks in Lhasa block suggest that they were probably derived from a phlogopite-bearing enriched mantle source related closely to metasomatism during earlier subduction events. The ultrapotassic rocks in southern Tibet may imply the uplift and extension of Tibetan Plateau after the collision of Indian plate and Eurasian plate. Meanwhile, there are a number of N-S grabens (rifts) mostly formed in 23~8 Ma in Lhasa block, which might have cut the lower crust or lithosphere into the depth, suggesting the extension of southern Tibet in Miocene.