The constituents of clay minerals in 11 soil profiles of Tibetan highland were identified by chemical analysis, canon-exchange capacity determination, differential thermal analysis and X-ray diffraction. The mineral constituents in the clay fractions of alpine and subalpine soils of northern Tibet are very similar, illite being predominant, accompanied with kaolinite and vermiculite and sometimes small amounts of chlorite and montmorillonite. Besides, some amorphous free iron oxide is also present in the surface layer of alpine soils. There ace significant differences in clay mineral constituents between the alpine and subalpine soils of southern Tibet. The clay fraction of alpine meadow soil derived from phyllite is similar to that of alpine soils in northern Tibet, but is quite different from that of subalpine soils derived from similar parent material, which contain greater amount of poorly crystallized kaolinite together with some vermiculite, gibbsite, mont-morillonite and interstratified mineral (12.6 Å). Except in the surface layer, the content of illite in the profile of subalpine meadow soil of southern Tibet is very low. Gibbsite usually accumulates in the upper horizons, while montmorillonite often found in the lower horizons. In the mountain shrub-steppe soils, the clay minerals consist mainly of an association of illite, kaolinite and vermiculite accompanied with montmorillonite, which increases in the calcareous layers, but no gibbsite is found. In the mountain podzolic soil from granite origin, illite, kaolinite and vermiculite occur in all horizons. Besides, a great amounts of montmorillonite accumulate in A₂,and gibbsite appears in the humus accumulating layer. The clay minerals of mountain brown forest soil (also from granite origin) consist mainly of illite, kaolinite, gibbsite and iron oxides, the amount of vermiculite and montmorillonite is small. It is very clear that the clay mineral constituents of the soils of Tibetan highland vary under different bio-climatic conditions. Illite occurs abundantly in the cool dry alpine tract, much vermiculite in the semiarid mountain regions along the River Tsanpo; while kaolinite and gibbsite in large amount in the warm moist region of southern Tibet.