A new isothermally based, cure kinetic model for the prepreg was presented using an industrially supplied prepreg rather than pure resin. The matrix resin was bismaleimide (BMI) resins, and the reinforcement was carbon fiber T700-12S. The BMI prepreg was measured from 170 to 220 degrees C by isothermal DSC. The isothermal cure reaction heat increases with the increment of cure temperature. The DSC data were analyzed by the proposed nth-order reaction model. An increase in reaction rate was observed at higher temperature in both neat and prepreg. After reaching the peak value, the reaction rate dropped off faster in prepreg, resulting in a lower average value of the ultimate heat of reaction. It was suggested the presence of carbon fiber had an effect on the cure kinetics as a heat sink. The carbon fibers imposed restrictions on the molecular mobility of the reactive species and did not change the cure mechanism. (c) 2005 Wiley Periodicals, Inc.