This study was aimed at using micro-Raman spectroscopy for the local characterisation of phase separated blends based on epoxy polymer and copolyethersulphone thermoplastic. The morphologies developed in the blends containing 25% by weight of thermoplastic were studied. The calibrations of the Raman data for the determination of the copolyethersulphone content and the epoxide conversion are presented in this paper and their applicability for spatially resolved Raman characterisation discussed. From spectra collected in both phases after increasing cure times, the evolution of the copolyethersulphone content in each phase was quantitatively determined, whilst a qualitative evolution of the epoxide conversion was obtained. To our knowledge, this study provided for the first time direct measurements of phase characteristics in thermoset-thermoplastic blends. (C) 2003 Elsevier Science Ltd. All rights reserved.