A polyimide blend system has been prepared from a base polyimide of BTDA-ODA by adding epsilon-caprolactam at the poly(amic acid) stage where epsilon-caprolactam undergoes polymerization to form nylon 6 during the thermal cyclodehydration of poly(amic acid). The blend has been characterized by elemental analysis, IP, C-13 CPMAS NMR, XRD and simple chemical methods. The thermal analysis study (TGA and DTA) shows that the stability of the blend systems is more in the lower temperature region (up to 300degreesC) in comparison to the control polyimide system. The isothermal study at 400degreesC in inert atmosphere shows that the blend system is equally stable but the isothermal study in air at 400degreesC shows that the thermooxidative stability of the blend films (except BB 4) is higher. Also. isothermal study in air at 500degreesC shows more than 90% weight loss for all the films within 3 h, but in an inert atmosphere, the blend films show lower weight loss compared to the control film. Although the XRD pattern of all the blend and control films shows an amorphous character, the films developed some crystallinity when treated with boiling NMP where the blend films developed higher crystallinity.