A large number of microgranular dioritic enclaves occur in some post-collisional metaluminous-peraluminous granites, which include Yebushan and Miao'ergou occurring respectively in eastern and western Junggar of North Xinjiang. Petrological and geochemical researches reveal the cogenetic relationship between the enclaves and the host granites. The microgranular enclaves having similar geochemical composition to host biotite granite in Yebushan were generated by the fractional crystallization of mantle-derived basic magma. By contrast, the enclaves hosted in Miao'ergou monzogranite seem to be restites resulting from partial melting of highly evolved basic rocks underplated in the lower crust during earlier mantle-derived magmatism. The enclaves carried by ascending acidic magma were assimilated and finally emplaced in the upper crust. Consequently, these enclaves in common with Junggar peralkaline granite are products of post-collisional magmatic activity in late-Paleozoic. The formation and evolution of both enclaves and host granites in Junggar region prove that the process of vertical growth of continental crust resulted from the underplating of post-collisional mantle-derived magmas in late-Pale-ozoic.