The performance of two module sets with the variation of pH was compared and determined. The permeate flux of two module sets was increased with the increment of TMP and energy consumption per membrane surface area on the whole range of pH. Permeabilities for linear and helical modules of first module set compared to D.I. water permeability were increased about 20% and 11% at pH 3.18, but decreased about 60%`s at pH 9.11 respectively. Permeabilities for linear and helical modules of second module set compared to D.I. water permeability were increased about 40% and 31% at pH 2.94, but decreased about 47% and 58% at pH 8.56 respectively. The highest permeabilities for the linear and helical module of first module set at pH 3.18 showed about 199% and 174% increment compared to lowest values at pH 9.11. The highest permeabilities for the linear and helical module of second module set at pH 2.94 showed about 163% and 212% increment compared to lowest values at pH 8.56. From these, pH is the variable which effects membrane performance.