In studying the characteristics of magnetite and other accessory minerals 'in various granitic rocks of Central-South Xizang, the author found that magi betites from different types of granites formed under different geological con- dlitions and of different ages have distinctly different characteristic features. The content and chemical composition of magnetite as well as the mineral assemblage and rare-earth pattern in the granite all reflect either the man- tle or crustal origin of the rock. It is concluded that the granodiorite in the Gangdise belt is characterized by mantle origin and the muscovite-biotite granite and tourmaline granite in Nielamu district are of crustal origin.