A new way for affinity chromatography has been developed to purify the McAb in ascites. Using nitrocellulose membrane(NCM) as solid-phase to adsorb the antigen, filtrating the sample under negative pressure through the NCM which could bind the relevant antibody to the antigen adsorbed on, then dissociating the antibody from the NCM in the purified form, this is the process of the so called membrane filtration affinity chromatography(MFAC). The albumin(Alb) McAb in ascites has been purified with the MFAC. The purified McAb showed a single band in the polyacrylamide gel electrophoresis(PAGE).While used in dot immunofiltration assay(DIFA) to detect Alb standard, the sensibility of the purified McAb was 20 times more than that of the ascites. The simple and effective MFAC can be used as a new affinity chromatography to purify antibodies in ascites.