Gas sparged ultrafiltration has been applied to a flat sheet membrane module and the enhancing effect from the injected bubbles is examined experimentally. Two membranes, polysulphone (PS) and polyethersulfone (PES), were used in the experiments, and four proteins, human serum albumin (HSA), human immunoglobulin G (IgG), bovine serum albumin (BSA) and lysozyme (Lys), were chosen as the test media. The effects of gas sparging on permeate flux, single protein transmission and protein fractionation have been investigated. Experimental results show that gas sparging can increase permeate flux and improve the efficiency of protein fractionation.