The standard (p∘=0.1MPa) molar enthalpies of formation, at T=298.15K, of 4-chloro-3-nitroaniline and 5-chloro-2-nitroaniline, in the condensed phase, were derived from their standard molar energies of combustion, in oxygen, to yield CO2(g), N2(g), and HCl·600H2O(l), measured by rotating bomb combustion calorimetry. From the temperature dependence of the vapour pressures of these compounds, measured by the Knudsen effusion technique, their standard molar enthalpies of sublimation, at T=298.15K, were derived by means of the Clausius–Clapeyron equation. The Calvet microcalorimetry was also used to measure the standard molar enthalpies of sublimation of these compounds, at T=298.15K. The combination of the standard molar enthalpies of formation in the condensed phases and the standard molar enthalpies of sublimation yielded the standard molar enthalpies of formation in the gaseous phase at T=298.15K for each isomer. Further, the standard (p∘=0.1MPa) molar enthalpies, entropies and Gibbs free energies of sublimation, at T=298.15K, were also derived. The standard molar enthalpies of formation, in the gaseous phase of all the chloronitroaniline isomers were also estimated by the Cox scheme and by the use of computational thermochemistry and compared with the available experimental values.