Fracture toughness of the polysulfone(PSf) film modified epoxy composite having a morphology spectrum was investigated. The epoxy resin was based on diglycidyl ether of bisphenol-A (DGEBA type) and diaminodiphenylsulfone (DDS). 1K carbon fabric was used as reinforceing material. The morphology spectrum which has gradual change of the morphological feature resulting from the concentration gradient of PSI in the composite can be obtained by inserting the PSf film in carbon fiber reinforced epoxy prepreg before cure. The relative rate of the dissolution and diffusion of the PSf in the epoxy determine the concentration gradient of the PSf. As the concentration of the PSf increases, the morphology changes from sea-island to nodular structure. The fracture toughness of the composite with 20 wt% PSf film was 2.7 times higher than that of the unmodified composite. This result was ascribed to the plastic deformation of the continuous PSf rich phase in the semi-IPN having morphology spectrum. (C) 2004 Elsevier Ltd. All rights reserved.