///The global expansion of C<SUB>4 plants during the Late Cenozoic is an important event in the Earth environmental-ecosystem evolution. Reconstructing the geological history of C4 plants holds a key in the understanding of the patterns and mechanisms of the Ceonzoic climate change, global floras evolution and the long-term variations in atmospheric CO2. Previous studies have demonstrated that during ca.7~4Ma, soil carbonate records (δ 13Csc)in the Chinese Loess Plateau display a southern-ward negative trend, indicative of a southern-ward expansion of C4 plants during the Late Miocene and the Early Pliocene. In this paper, the authors report a study based on δ 13Csc of loess-red clay sequence from the Baishui and Zhuanglang sections near the Liupanshan region, and the result shows that C4 plants expansion may have initiated as early as at ca. 20 Ma with C4 component up to 15 % ~40 % during the Miocene.