Activated carbons with high surface area, large pore volume, and high mesoporosity were prepared from herb residues. The raw material was treated by 0.5 M NaOH solution and activated under vacuum using ZnCl2 as the activation agent. Four activated carbons obtained under different preparation conditions were compared in detail. It was found that both the vacuum condition and base-leaching process have positive effects on the specific surface area and mesopore structure characteristics. The Brunauer-Emmett-Teller (BET) surface area and total pore volume of the activated carbon obtained by combining vacuum condition and base-leaching method have increased by 125.3% and 64.9% respectively comparing with those of activated carbon prepared under atmosphere without base-leaching. With an activation temperature of 450 degrees C and an impregnation ratio of 2.5, activated carbon with a BET surface area of 1952 m(2)/g, a total pore volume of 1.479 cm(3)/g, and a mesoporosity of 98.0% was obtained. The thermal decomposition properties of raw materials and activated carbons were studied. Furthermore, the effects of preparation parameters such as activation temperature and impregnation ratio on the properties of activated carbons were investigated. The scanning electron microscopy images of the activated carbon showed a porous structure. (C) 2010 Elsevier B.V. All rights reserved.