Abstract: Porosities of 4 biomass chars of rice hull,tree leaf,cornstalk and cotton stem were studied using the N2 adsorption method.The special surface area(SSA) and pore size distribution were obtained for the samples.The results showed that there were significant differences in SSA and pore size distribution among the biomass chars.The largest SSA was 242.21 m2g-1,while the smallest 0.81 m2g-1.At the pyrolysis temperature of 850℃,the pore size distributions of rice hull,tree leaf and cornstalk char peaked in the micropore and the mesopore ranges.In contrast,the cotton stalk char had only one peak in the mesopore range.The pyrolysis temperature considerably affected the porosity.Synchronous heating resulted in larger SSA and more fine pores than asynchronous condition.In this study,it was found that chars obtained at 600℃ or 850℃for rice hull and 850℃ for tree leaves had the largest SSA.Therefore,they were considered more suitable to be used as adsorbents.