Polyimide (PI) aerogels containing rigid-rod biphenyl, benzimidazole, and triphenylpyridine moieties have been developed. The flexible PI aerogels exhibited excellent thermal stability with glass-transition temperatures (T-g) higher than 350 degrees C. Initial porous structures in the PI aerogels could be maintained even after isothermal aging at 300 degrees C for 24 h in nitrogen. Furthermore, the weight losses of the aerogels after isothermal aging at 300 and 400 degrees C for 24 h in nitrogen were below 5 and 10 wt %, respectively.