The main objective of this study is to test the suitability of commercial poly(vinyl chloride) (PVC) as a membrane material for ultrafiltration(UF) application, and futhermore, to find the suitable conditions for the membrane formation. Asymmetric PVC membranes have been prepared by immersion pricipitation technique. The functions and characteristics of the membranes could be adjusted by changing the molecular weight of PVC, the composition of the casting solution, the kinds of the solvent and the precipitating agent, and the temperature of the non-solvents. The water content within the membrane, water flux, and solute (dextran) rejection were experimentally measured. In order to understand the mechanism of membrane formation, the effect of the precipitation path on membrane performance has additionally been investigated using the ternary phase diagram of the polymer/solvent/non-solvent system. Finally the anisotropic structure of the membranes has been confirmed using the scanning electron microscope.