Abstract: Lemon peel as the adsorbent was studied for its ability to remove the anionic dye Congo red. The effect of adsorbent dosage, contact time, initial concentration of Congo red and temperature on the adsorption was investigated. The results showed that the adsorption capacity of Congo red on lemon peel decreased with the increase of adsorbent dosage and temperature, while it increased as the initial concentration of Congo red increases. The biosorption of lemon peel to Congo red fits in the Langmuir isotherm model; The sorption kinetics of Congo red on lemon peel obeys the Pseudo-Second-order Model; The thermodynamic parameters calculated indicate that the adsorption is a spontaneous exothermic process.