Seasonality changes in China under elevated atmospheric CO2 concentrations were simulated using nine global climate models, assuming a 1% per year increase in atmospheric CO2. Simulations of 20th century experiments of season changes in China from the periods 1961-80 to 1981-2000 were also assessed using the same models. The results show that the ensemble mean simulation of the nine models performs better than that of an individual model simulation. Compared the mean climatology of the last 20 years in the CO2-quadrupling experiments with that in the CO2-doubling ones, the ensemble mean results show that the hottest/coldest continuous-90-day (local summer/winter) mean temperature increased by 3.4/4.5℃, 2.7/2.9℃, and 2.9/4.1℃ in Northeast (NE), Southwest (SW), and Southeast (SE) China,respectively, indicating a weakening seasonal amplitude (SA), but by 4.4/4.0℃ in Northwest (NW) China, indicating an enlarging SA. The local summer lengthened by 37/30/66/54 days in NW, NE, SW, and SE China, respectively. In some models, the winter disappeared during the CO2-quadrupling period, judging by the threshold based on the CO2-doubling period. The average of the other model simulations show that the local winter shortened by 42/36/61/44 days respectively, in the previously mentioned regions.