Increasing demands to decrease engine weight and improve engine performance has led to an investigation to develop polymer composites capable of being used at 371-degrees-C and above in 4 atmospheres of air. The results of an investigation to determine the thermo-oxidative stability (TOS) of various fluorinated polyimides, 3F-PDA, 36F-PDA, Avimid-N, AFR700B, and other PMR-type resins and graphite composites containing these polyimides at 371-degrees-C in air at 1 and 4 atmospheres are presented. Weight losses due to aging under these conditions are presented as the criteria for measuring the TOS. The data show that 3F-PDA and Avimid-N which have equivalent TOS, exhibit twice the TOS than that of AFR700B and other PMR-type resins. 36F-PDA exhibits even better TOS than 3F-PDA or Avimid-N.