The effects of plasma treatment of pyromellitic dianhydride-4,4＇-oxydianiline polyimide (PMDA-ODA PI) on the adhesion strength of novolac epoxy resin/PMDA-ODA PI joints were studied. The adhesion strength of novolac epoxy resin/PMDA-ODA PI joints increased by plasma treatment of PMDA-ODA PI. Oxygen and argon plasmas were better than ammonia plasma in improving the adhesion strength. However, the adhesion strength decreased by aging oxygen and argon treated PMDA-ODA PI above 150 degrees C and ammonia treated PMDA-ODA PI above 250 degrees C, which was not correlated with the surface energy of thermally aged plasma treated PMDA-ODA PI. The failure mode of the joints was found to be cohesive in the PMDA-ODA PI layer very close to the interface. The adhesion mechanism of novolac epoxy resin/plasma treated PMDA-ODA PI joints was investigated and the decrease of adhesion strength by thermally aging the plasma treated PMDA-ODA PI was examined.