Carbon fibre-reinforced thermoplastic composites laminates (CFRP) meant for fusion bonding have been moulded using different release media. The potential contamination of the laminate surface by the release media and its effect on the mechanical performance of fusion bonded joints was studied. The physical and chemical state of the bonding surface were analysed with surface energy and roughness measurements. The chemical composition of the laminate surfaces has been investigated by X-ray photoelectron spectroscopy (XPS). The laminates were then fusion bonded through co-consolidation. The mechanical performance of the bonds was studied by a mode I fracture toughness measurement using the double cantilever beam (DCB) test. The results show significant effect of contaminations on mechanical performance of the joints.