In this work, bio-char, a mass productive by-product of biomass fast pyrolysis, was adopted as an adsorbent to remove tetracycline (TC) from aqueous solution. To enhance the adsorption capacity, a simple modification of bio-char with acid and alkali was carried out. Bio-char samples were characterized by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption-desorption isotherm. The results show that the alkali treated bio-char possesses larger surface area than those of raw and acid treated bio-chars, and accordingly exhibits a more excellent adsorption performance (58.8 mg/g) than the other two bio-chars and other adsorbents reported previously. The graphite-like structure of bio-char facilitates the formation of pi-pi interactions between ring structure in tetracycline molecule and graphite-like sheets. The surface area showed significant effects on TC adsorption as well as O-containing functional groups, whereas the initial pH of solution has small effects on TC adsorption under the experimental conditions. (C) 2012 Elsevier Ltd. All rights reserved.