An innovative research effort has been directed at developing a high-temperature-resistant polymer matrix composite in responding to the need of high specific strength/stiffness materials at elevated service temperatures for high-speed-flight vehicles. A new polyimide with glass transition temperature Tg = 511°C, designated as CSPI (Chung Shan modified Poly-Imide) and its composite reinforced with carbon fiber have been developed by the Material Research and Development Center of the Chung Shan Institute of Science and Technology (MR/DC, CSIST, Taiwan, R.O.C.). The purpose of this paper is to show the high-temperature properties of this carbon/CSPI composite and compare its high-temperature-resistant capability with the conventional carbon/PMR-15 composite. The composites characterization work, including physical, mechanical (static and fatigue) and thermal cycling behaviors at room and elevated temperatures up to 450°C, have been carried out for both carbon/CSPI and conventional carbon/PMR-15 unidirectional and quasi-isotropic laminates. The research results have demonstrated that the carbon/CSPI composites exhibit unique high-temperature characteristics and performance and have high potential for application in supersonic and hypersonic flight vehicles.