In the present study, biomass of Agaricus campestris was tested to evaluate its effectivity as a biosorbent for the removal of Cr (VI) ions from aqueous solutions. The influence of various process parameters such as pH, temperature, contact time, biosorbent dosage and desorption were studied. Pseudo-first order, pseudo-second order, Ritchies and intraparticle diffusion model were used to present the adsorption kinetics. Results obtained indicate that the adsorption process is fast and spontaneous within the first 60 min. The experimental data supports pseudo-second order model. The sorption data conformed well to the Langmuir isotherm model. The maximum adsorption capacity (q(max)) onto A. campestris was 56.21 mg g(-1) for Cr(VI) at 45 degrees C when 0.1 g biomass was used. In addition, the mean values of thermodynamic parameters of standard free energy (Delta G(0) = -1.635 kJ mol(-1) at 45 degrees C), standard enthalpy (Delta H-0 = -9.582 kJ mol(-1)) and standard entropy (Delta S-0 = -24.992 J mol(-1)K(-1)) of the adsorption mechanism were determined.