Microporous polyethersulfone (PES) flat-sheet membranes were successfully prepared by reverse thermally induced phase separation (RTIPS) in which the membrane-forming system that was employed featured a low critical solution temperature (LCST) and consisted of PES, N,N-dimethylacetamide (DMAc) and polyethylene glycol (PEG200). Light transmittance was used to follow the cloud point and precipitation rate of the casting solution during the RTIPS process. The morphology of the formed membranes was investigated using scanning electron microscopy (SEM); the corresponding permeation properties of the membranes, such as pure water permeation flux, rejection rate and mechanical properties were also investigated. The results showed that the cloud point decreased with the increasing mass ratio of PEG200/DMAc. SEM images revealed that the membrane structure could be changed from exhibiting finger-like pores to exhibiting a bicontinuous structure along its cross-section using the RTIPS process; it was also observed that the dense skin layer was converted to a porous surface. It was concluded that membranes which prepared by the RTIPS process have a low ratio of maximum pore size to mean pore size. A PES flat-sheet microporous membrane with a higher pure water permeation flux of 1040 L m(-2) h(-1) (0.1 MPa) was obtained via the RTIPS method described in this work. Moreover, with the same mass ratio of PEG200/DMAc, the mechanical strengths of membranes prepared via RTIPS were better than those prepared by the nonsolvent induced phase separation (NIPS) method. (c) 2013 Elsevier B.V. All rights reserved.