The vapor pressure for crystalline E-caprolactam (CAS Registry No. 105602) was measured by the Knudsen method in the temperature range (293 to 338) K with a modified effusion cell with enlarged sublimation surface and by the transpiration method between T = (302 and 339) K. The latter method was also used to measure the vapor pressures of the liquid phase between T = (345 and 373) K. The thermodynamic parameters of sublimation and of vaporization and the standard entropy of caprolactam in the ideal gas state were estimated from the obtained data. Calculations of the thermodynamic properties of caprolactam in the ideal gas state were carried out based on the molecular data and the results obtained by DFT (B3LYP/6-311G*) quantum-mechanical calculations. The experimental and calculated values of the entropy of gaseous caprolactam agree with each other within 0.2 % at 298 K.