Carbon/polyimide composites can be used for high temperature resistant materials with high thermo-oxidatively stable materials. PMR-15 polyimide was synthesized from the three monomer reactants, NE(5-norbonene-2,3-dicarboxylic monomethylester), BTDE(3,3'',4,4''-benzophenone tetracarboxylic dimethylester) and MDA (4,4''-methylene dianiline). In this study, changes in chemical structure, molecular weight, viscoelastic behavior, and voltile materials of the PMR-15 polyimide composites during the cure reaction were investigated for establishing an optimum manufacturing condition. From the results of analysis, a 2-step compression molding process can be established for the polymide composites. In the first step, a vaccum bag mold (with a vacuum hole in the press) was heated up to 210℃ for degassing the volatiles and by-products, and kept at 210℃ for 60 minutes for pre-imidization. In the second step, composites were compressed at 255℃ for proper lamination and stabilized at 320℃ for cross-linking reactions. The resulting composites showed excellent physical properties with the void-free feature. Post cure effects on the mechanical and thermal properties of laminated composites were examined as a function of time at 350℃. glass transition temperature (T_g) and thermal degradation starting temperature (T_d) increased with the post-cure time whereas the transverse tensile strength decreased slightly.