lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai (35°N), the Loess Plateau. Stable carbon isotopic composition indicates that ( ⅰ ) C_4 plants might be present at least by7.0 Ma; ( ⅱ ) C_4 plants expanded gradually between ～4.0 and ～3.2 Ma, and their biomass fraction was up to 50%; and ( ⅲ ) the biomass of C_4 vegetation since ～2.0 Ma seems to have been decreased to the level (about 20%) before 4.0 Ma. C_4 plant expansion at Lingtai cannot be fully understood with the “global C_4 expansion” model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C_3/C_4 shift except changes in atmospheric CO_2 concentrations and temperature. The latitudinal zone for C_3/C_4 transition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N is the ideal boundary lsotopic analyzes for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai (35 ° N), the Loess Plateau. Stable carbon isotopic composition that (i) C_4 plants might be present at at least 7.0 Ma; (ii) C_4 plants increased from ~ 4.0 and ~ 3.2 Ma, and their biomass fraction was up to 50%; and (iii) the biomass of C_4 vegetation since ~ 2.0 Ma seems to have been decreased to the level (about 20%) before 4.0 Ma. C_4 plant expansion at Lingtai can not be fully understood with the “global C_4 expansion” model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C_3 / C_4 shift except changes in atmospheric CO_2 concentrations and temperature. The latitudinal zone for C_3 / C_4 transition seems to move southwards slightly in East Asia, compared with the case in North America where 37 ° N is the ideal boundary