In this work the kinetic of degradation of methylene blue (MB) by Fenton process was studied. The effect of some parameters such as H₂O₂, Fe²⁺ and MB concentration were investigated. The results indicate that the rate of degradation increases with increasing H₂O₂ concentration up to 0.001 M, but further increase of H₂O₂ concentration decreases the degradation rate. The degradation rate increased with increase in MB and Fe²⁺ concentrations. The order of the reaction with respect to each reactant was determined by the initial rate method. Also the activation energy of the degradation of MB was determined to be 89.8 kJ∙mol^-1.