Two immiscible polymers, polyetherimide (PEI) and polysulfone (PSf), were used to prepare PSf microfiltration membrane in a co-casting process. PEI/NMP and PSf/PVP/NMP were employed as the coating and support solutions, respectively. The origin of the delamination/adhesion in the PEI/PSf composite membranes was investigated. Light transmission, coagulation value, membrane shrinkage, movement of the phase separation frontier and Scanning Electron Microscopy were utilized to unravel the adhesion and delamination mechanism. It was found that the difference in shrinkage values of different layers determined adhesion/delamination. With the increase of coagulation bath temperature, the difference in thickness shrinkage values of PEI and PSf membranes became smaller, and the morphology of double layer also changed from delamination to adhesion at temperature above 65 degrees C. The effect of coagulant value (CV) for the system studied appeared to be insignificant in relation to the adhesion/delamination. (C) 2010 Elsevier B.V. All rights reserved.