Sulfonated polysulfone (SPS) was synthesized from polysulfone resin using sulfuric anhydride-triethyl phosphate complex. The SPS was dissolved in N-methyl-2-pyrrolidone (NMP) using LiNO3 as a swelling agent. The resultant SPS dope was casted on a glass plate. An optimum ratio of SPS, NMP and LiNO3 was 1:5:0.2 for making an UF membrane. The solvent was evaporated for 30 min, at 338 K, and an ultrafiltration membrane was obtained by gelation in an ice-cold bath. The ceramic/SPS composite membrane was prepared by the following original procedure. First, the pores of the ceramic support were plugged with chitosan suspension at a pH over 6. The SPS dope was thinly coated on the membrane surface, and then the membrane was gelled in an ice-cold bath under pH 6. The chitosan suspension plugged in the pores was removed because the chitosan became soluble under pH 6. Thus, the composite membrane having negatively charged layer was obtained without plugging the ceramic support pores. The composite membrane showed a high pure water flux of 39.5 x 10(-6) m(3) m(-1) s(-1) at an applied pressure of 100 kPa and a molecular weight cut-off of 20 000.