Two different epoxy based prepreg systems were characterized and compared using thermal analysis. A prepreg system presently used in the commercial airplane industry was compared with a prepreg system that is a prospective candidate for the same applications. The commercial system in use is a controlled flow resin prepreg system which is a 177 degrees C cure system, while the prospective prepreg system is marketed as a dual prepreg system that can be cured at either 121 degrees C or 177 degrees C. Thermal characterization techniques including differential scanning calorimetry (DSC), dielectric analysis (DEA), and dynamic mechanical analysis (DMA) were used to investigate these systems. The difference in the curing mechanisms of both prepreg systems were identified through these thermal analysis techniques. Although, the kinetics of these systems were found to be vastly different their heats of reactions were very similar. The activation energies for the prepreg systems were determined by DSC using Kissinger’s method and were found to be quite different. DMA measurements on autoclave cured composites demonstrated that the prepregs obtained a different degree of cure as well as different glass transition temperatures (T-g). Furthermore, the use of DEA and DMA demonstrated a difference in gelation of the two prepreg systems examined.