A novel diacyl chloride monomer dimethyl (3,5-bis(chlorocarbonyl) phenyl) phosphonate (compound(I)) with a phosphonate group (-PO(OCH3)(2)) was successfully synthesized and then blended with 2,2', 4,4'-biphenyl tetraacyl chloride (BTEC) as organic phase monomers to prepare RO membranes for brackish water desalination. BM-X was utilized to represent RO membranes prepared by compound (I). X represented the concentration percent of compound (I) (%) in Isopar G solutions, which was the ratio of the concentration of compound (I) to the concentrations of compound (I) and BTEC. When X increased from 0% to 50%, the water flux of BM-X improved from 35 L/m(2)h to 79 L/m(2)h while holding high salt rejections (99.1-99.5%). The enhancement of membrane hydrophilicity was certified by the contact angle decreasing from 83 degrees to 38 degrees with compound (I) content increasing from 0% to 50%. Because the improvement of membrane hydrophilicity made for the enhancement of membrane antifouling, BM-50 exhibited a lower water flux decline and irreversible fouling degree compared with a commercial RO membrane (BW30FR, Dow Filmtec). The irreversible fouling degree reached 6.8% after 1500 min three cycles fouling which was lower than 14.1% of BW30FR. Finally, BM-50 showed a very good and stable desalination performance for 30 days measured in a pH=6.0 and 2000 ppm NaCl solution.