Size distribution in sediments of Qinghai Lake is mainly silt grade, with finer in lake sediment, coarser in lake bank sediment. Clay minerals are mainly illite and chlorite, with little montmorillonite and trace kaolinite. But montmonillonite is not observed in ground sediment. The chemical composition of clay in Qinghai Lake is similar to that for sea clay. The data of clay are useful for studing sedimentary environment and condition, in particular Al2O3/MgO ratio in clay.