An experimental study was undertaken to investigate the mechanical response of the graphite fiber reinforced thermoplastic polyimide composite IM7/LaRC^™-PETI-5 for use in long term durability tests. Composite panels were prepared using unidirectional prepreg and regions of different resin consolidation were identified using a nondestructive ultrasonic technique. Specimens representing four different degrees of resin consolidation were tested at room temperature in tension, compression, and flexure in the as-received state, as well as isothermally exposed for 1500 h at 177°C, and isothermally exposed to a “hot/wet” environment (80°C, 90%+ relative humidity). Results showed that specimens tested in tension and compression had a higher dependence on resin consolidation than those tested in flexure. However, specimens tested in flexure showed a greater property degradation from environmental exposure due to a lack of resin consolidation.