The aim of this work was finding optimum cleaning agents and conditions for cleaning reverse osmosis (RO) and nanofiltration (NF) membranes fouled by licorice aqueous solutions. The effect of various chemicals on flux recovery (FR) and resistance removal (RR) of the fouled membranes was investigated. For both membranes the results indicate that a combination of ethylene diamine tetra acetic acid (EDTA), sodium dodecyl sulphate (SDS) and sodium hydroxide may be used as cleaning agents to achieve an optimum cleaning efficiency. Zeta potential and contact angle measurements indicate the changes in charge and hydrophilicity of the surface of RO and NF membranes at various pH solutions, respectively. The effect of surface characteristics is evident in efforts to select the optimal operating conditions. The effect of cleaning condition such as concentration, temperature, pH and cleaning time was studied. The optimum temperature, cleaning time, pH and concentration were found as 35 +/- 1 degrees C, 20 min, 12 and 0.1 wt.%, respectively. SEM pictures showed the surface morphology of RO and NF membrane. (C) 2010 Elsevier B.V. All rights reserved.