In this work experimental vapor pressures of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) were measured with transpiration method. Corresponding enthalpies of sublimation were determined to be (130.9 � 2.1) kJ mol À 1 and (108.1 � 1.6) kJ mol À 1 , respectively. Along with the experimental data fitting equations are reported and p-T data extrapolated to 298.15 K to be 0.71 μPa for RDX and 823 μPa for TNX.