Submerged hollow fiber membrane system is widely used in water and wastewater treatment plants. One of the major problems of the microfiltration/ultrafiltration (MF/UF) process is membrane fouling. Few techniques have been developed to reduce membrane fouling and increase critical flux of the filtration process. In this study, membrane vibration was applied to improve the critical flux in a submerged hollow fiber MF system. A bench scale unit was especially built for this purpose and different vibrating speed was tested. The effect of the feed concentration and vibrating speed on the critical flux measurement were investigated. The critical flux was measured at different vibrating speeds varied from 0-500 oscillation per minute (opm) (5.83Hz). The lowest critical flux was 15L center dot m-2 center dot h-1 when no membrane vibration was used and then increased gradually from 27 to 56L center dot m-2 center dot h-1 when the vibrating speed increased from 100 to 500opm (8.35Hz). A sharp drop in the critical flux was noticed when the concentration of feed suspension doubled from 5g/L to 10g/L. However, the increase in the critical flux was insignificant at higher feed concentration even when a high membrane vibrating speed was applied. This signifies that there is a limit for flux improvement in a vibratory system which is strongly dependent on the feed concentration.