AbstractTo measure tritium pressure in fuel processing systems in DT burning fusion devices, the applicability of a bremsstrahlung counting method was examined by using an apparatus for supply and recovery of highly concentrated tritium gas. For the measurement of bremsstrahlung, a newly designed proportional counter showed a considerably high sensitivity to the measurement of bremsstrahlung. In addition, the bremsstrahlung counting rate showed excellent linearity to tritium partial pressure when the total pressure was below 100 Torr. Above this upper pressure limit, the counting rate deviated downward from the linear relation. The deviation, however, could be represented quite well by a simple exponential function of pressure. It was shown that the tritium partial pressure in the hydrogen isotope gases could be determined in the range from 5 × 10−2 to 760 Torr. Consequently, the present methods is quite useful for in-situ and non-destructive measurements of tritium partial pressure in the fuel processing systems of thermo-nuclear fusion devices.