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(-1)and (108.1 +/- 1.6) kJ mol(-1), respectively. Along with the experimental data fitting equations are reported andp-Tdata extrapolated to 298.15 K to be 0.71 mu Pa for RDX and 823 mu Pa for TNX.