In this study, asymmetric cellulose acetate (CA) membranes were prepared from polymeric blend of CA-PEG/1-methyl-2-pyrrolidone (NMP) system via phase inversion induced by immersion precipitation in water coagulation bath. Effects of PEG concentration (0 wt.%, 5 wt.% and 10 wt.%) and coagulation bath temperature (CRT = 0 degrees C and 25 degrees C) on morphology, pure water permeation flux (PWF) and thermal/chemical stability of the prepared membranes were studied and discussed. Rejection of the developed CA membranes was quantified using human serum albumin (HSA) solution. Increasing PEG concentration in the cast solution film along with higher CBT results in increasing the membrane thickness, pure water flux (PWF) and HSA transmission, also these changes facilitate macrovoids formation (even with the size of more than 50 pm) in the membrane sublayer. On the other hand, increasing PEG concentration along with reduction of CBT results in increasing the thermal/chemical stability of the prepared membranes. Presence of low molecular weight PEG additive in the cast solution film increases porosity/permeability and simultaneously thermal/chemical stability of the prepared membranes. On the other hand, using cold coagulation bath despite of increasing the thermal/chemical stability of the prepared membranes results in reduction of membranes porosity/permeability. (C) 2010 Elsevier B.V. All rights reserved.