Carbon fibre/vinyl eater composites were made from sized carbon fibres. The carbon fibres were sized with an in-house sizing process and then formed into a unidirectional fabric. This fabric was processed into composite panels by a resin film infusion (RFI) technique. The effects of two dissimilar sizing agents--a brittle thermoplastic K-17 poly(vinyl pyrrolidone) (PVP) and a ductile thermoplastic polyhydroxyether (phenoxy resin)--on notched fatigue, short-beam shear, transverse flexure properties and compression properties were studied.The fatigue properties of carbon fibre/vinyl eater composites were influenced drastically by the type of sizing agent used. A 20-fold increase in lifetime was demonstrated at a loading level of 207 MPa for the ductile phenoxy sized composite compared with the unsized composite. The brittle PVP sized composite panel showed a sixfold increase in lifetime compared with the unisized case. The phenoxy-sized composite panel showed a 40% increase in flexural modulus and the PVP-sized panel showed a 20% increase compared with the unsized composite panels. Negligible differences in the shear strength, flexural strength and static compressive strength were observed for the different interphase agents. The implications of these results for tailoring polymeric interphases in vinyl-ester-matrix composites are discussed.