Humification coeff icients of organic materials and annual mineralizat ion of soil organic carbon were determined in f ield experiments.Amounts of organic materials application were estimated by statistical data to analyze input and output of organic carbon pools in typical arable soils in important agricultural areas of Eastern China in order to evaluate preliminarily.their functions as source or sink of atmospheric CO₂.Humification coefficients in arable soils of agricultural areas of Eastern China changed in the order: Songnen plain (crop straw 0.37, crop roots 0.47, green manure 0.26, livestock manure 0.54) > Red soil hilly region (with corresponding values of 0.28, 0.45, 0.25, 0.42) > Xialiaohe plain (values: 0.35, 0.39, 0.22, 0.33) > Huanghuaihai plain (values: 0.25, 0.32, 0.18, 0.27).Humification coefficient did not changed proportionately with temperature and rainfall and was multiply influenced by environmental factors, especially soil properties.Under realist ic application of organic materials, Songnen plain, Xialiaohe plain, Huanghuaihai plain and Red soil hilly region would have a soil organic carbon formation annually of 538.0 kg hm^-2, 679.7 kg hm^-2, 760.7 kg hm^-2 and 1 059.7 kg hm^-2.Annual mineralizat ion amounts of soil organic carbon are 905.3 kg hm^-2, 723.5 kg hm^-2, 723.1 kg hm^-2 and 782.9 kg hm^-2, respectively.The C balance, calculated as the difference between input and output of soil organic carbon, suggested a deficit (decreasing organic C) in the arable soil of Songnen plain, an increasing organic C content in the paddy soil of Red soil hilly region, an equilibrium in arable soils of Xialiaohe and Huanghuaihai plains.These values determine their funct ions as source or sink of atmopheric CO₂.