Physical and chemical modifications of polymeric ultrafiltration membranes are necessary to improve their hydrophilic properties, strength, and other characteristics. Microcrystalline cellulose (MCC) was prepared from cellulose pulp by acid-catalyzed hydrolysis in the presence of ultrasonic radiation, and the properties of MCC were evaluated. Through the addition of MCC to a polysulfone (PS) membrane Solution, a casting solution of a PS/MCC blend was obtained. Subsequently, the Ultrafiltration membrane from the blend was further developed in a phase-inversion process comprising immersion and deposition. The capacity for Ultrafiltration was better with increasing MCC content. When the ratio of MCC to PS was 0.3, the pure water flux of the composite membrane reached 234.2 L/m(2)/h, and the retention of a bovine serum albumin Solution (1 g/L) was as high as 93.4%. The membranes were also observed with scanning electron microscopy and atomic force microscopy to study their microstructures. (c) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 550-556, 2009