Thermal stresses have been measured in single carbon fibre polypropylene matrix composites using micro Raman spectroscopy. The study focuses on the influence of a transcrystalline interlayer on the thermal residual stress distribution in composites. A series of three experiments were made in order to systematically study the influence of thermal history, transcrystalline interlayer thickness and matrix supermolecular structure. From the experiments it was shown that the transcrystalline interlayer results in higher thermal residual shear stress. This was explained by anisotropy in the transcrystalline interlayer resulting in higher radial thermal expansion and thus higher radial stress. (C) 2003 Kluwer Academic Publishers.