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Laboratory measurements were conducted with a chamber to determine the size distribution and scattering coefficient of aerosol emitted from the rice straw and corn stover burning，two major agricultural residues in China. The size distributions of those rice-burned and corn-burned aerosols are well characterized by unimodal lognormal functions，with a remarkable feature of accumulation mode. The fresh smokes’ median diameters of number distribution centered at 0.15±0.03μm，0.22±0.01μm for rice-burned and corn-burned aerosols，respectively. PM0.5contributes up to 91％ among PM10 for rice-burned aerosols，and 99％ for corn-burned aerosols. During smoke age，the median diameter of number distribution shows an approximate logarithm increase for rice-burned aerosol with the time of number concentration decreasing to the half of its initial value about 240 min from 0.15μm to 0.27μm. Whereas，the median diameter of number distribution shows a nearly linear increase for corn-burned aerosol with the time of number concentration decreasing to the half of its initial value about 120 min from 0.22μm to 0.28μm. The evolution of scattering coefficient at 545nm matches parallel to the total surface areas per cubic centimeter of aged aerosols. It indicates smoke age is an important process to influence the size distribution and optical property of aerosols. The emission factors in particle phase are 7.7±1.9×1015particles kg-1，1.2±0.4×1016particles kg-1for rice straw and corn stover burnings，respectively.