This work is conducted to chemical treatment for improved performance of menbrane(RO). CPA2 and SWC1 membranes were soaked under controlled conditions of temperature in solutions of hydrofluoric acid(HF), fluosilicic acid(FSA) and isopropyl alcohol(IPA) in water. The flux of CAP2 membranes increases about 4 d with 15 wt% HF which appears to be optimum. The rejection surprisingly also increases to about 98.7% at 200 psi after exposure for that period. Chemical treatment with 15 wt% of SWC1 membranes also yields a flux increase of about 83% with an optimum treatment time 3 d. The rejection increases slightly during the treatment period.