Abstract: Four biomass of rice straw (RS), rice husk (RH), wood chips (WC) and cotton straw (CS) were chosen to prepare biomass chars which characterized by nitrogen adsorption/desorption and Fourier transform infrared spectroscopy (FT-IR). The influence of biomass type and pyrolysis temperature on pore structure and surface chemical properties of the chars was investigated. Mercury adsorption experiments were carried out in a fixed-bed reactor. The results show that specific surface area, micro-pore volume and fractal dimension of the biomass chars increase firstly and then decrease with increase of the pyrolysis temperature. With the pyrolysis temperature increasing, both the quantity and sorts of the superficial functional groups on the biomass chars reduce and they are dependent greatly on the biomass sorts. Both the superficial functional groups and contents of RH600 and RS600 are more abundant than that of WC600 and CS600. It is not simply direct relationship among the mercury adsorption capacity, the micro-pore volume and the fractal dimension of the biomass chars. It is supposed that the oxygen contained functional group may have dominant effect on the mercury adsorption.