Activated carbons were produced from reedy grass leaves by chemical activation with H3PO4in N2atmo-sphere and their characteristics were investigated. The effects of activation temperature and time wereexamined. Adsorption capacity was demonstrated with BET and iodine number. Micropore volume andpore size distribution of activated carbons were characterized by N2adsorption isotherms. The surfacearea and iodine number of the activated carbons produced at 500◦C for 2 h were 1474 m2/g and 1128 mg/g,respectively. Thermal decomposition of pure reedy grass leaves and H3PO4-impregnated reedy grassleaves have been investigated with thermogravimetric/mass spectroscopy (TG–MS) technique. It wasfound that the temperature and intensity of maximum evolution of H2O and CO2of H3PO4-impregnatedreedy grass leaves were lower than that of pure reedy grass leaves. This implies that H3PO4as an activat-ing reagent changed the thermal degradation of the reedy grass leaves, stabilized the cellulose structure,leading to a subsequent change in the evolution of porosity. The results of X-ray photoelectron spec-troscopy and Fourier-infrared spectroscopy analysis indicate that the produced activated carbons haverich functional groups on surface.