Biomass activated carbons were activated and pyrolyzed at 300–800 °C under nitrogen circumstance (named as CAC300–CAC800). The physicochemical characteristics of CACs and mechanisms of perchlorate (ClO₄⁻) adsorption on CACs were investigated. Compared to CAC300, CAC600–CAC800 had higher surface area, total prove volume, higher hydrophobic surface and an abundant of oxygen-containing groups (–COH and –COOH) which contributed to a higher ClO₄⁻ adsorption capacity. The pH value of solution significantly affected ClO₄⁻ adsorption and the maximum ClO₄⁻ adsorption capacity occurred at pH 2.0 (less than pH_IEP), where surface charge was positive. Electrostatic attraction and hydrogen bonding to oxygen-containing groups on CACs were considered as the dominant force for ClO₄⁻ adsorption. With the pH increased, electrostatic attraction disappeared and surface oxygen-containing groups were gradually deprotonated, and the ClO₄⁻ adsorption amount was gradually decreased few until pH 12.0. The batch adsorption experiments of ClO₄⁻ showed that CAC600–CAC800 were effective adsorbents for the adsorption of ClO₄⁻.