Crosslinked polyethylene glycol/polyetherimide (PEG/PEI) composite membranes were prepared, in which asymmetric PEI membrane prepared with phase inversion method acted as the microporous supporting layer in the flat-plate composite membrane. The different function compositions of the PEG/PEI composite membranes were characterized by reflection FTIR. The surface and section of PEG/PEI composite membranes were investigated by scanning electron microscope (SEM). The composite membranes prepared in this work were employed in pervaporation separation of ethyl thioether/heptane mixtures. Swelling experiments were carried out in ethyl thioether/heptane mixtures to investigate the stable behavior of the membranes. Effects of amount of PEG, crosslinking temperature, amount of crosslinking agent and crosslinking time on the separation efficiency of ethyl thioether/heptane mixtures were studied experimentally. Experiment results demonstrated that crosslinking temperature at 80-100 degrees C was more preferable, the amount of crosslinking agent was up to 16 wt%, and PEG amount at 14 wt% was optimal as far as flux and sulfur enrichment factor was concerned. In addition, the stability of composite membrane during long time operation was studied, which could be expected that the membrane prepared in the work should be used to separate ethyl thioether/heptane mixtures in real application. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.