The interface bonding of graphite fiber/epcxy resin has been investigated. The acidic groups on the graphite fiber surface were determined by flow microcalorime-try after oxidation treatment with nitric acid. There is a good correlation beween the concentration of the acidic groups and the interlaminar shear strength of the composites

which decreases as the acidic groups are reduced by heating in a hydrogen stream.Prom these experimental results

it was justified that the chemical reaction oc-cured between the epoxy resin and the acidic groups of the surface of the graphite fiber is responsible for the interface bonding.