The standard molar energy of combustion of 9-hydroxy-1, 4-anthraquinone and 9-methoxy-1, 4-anthraquinone were determined with a static-bomb calorimeter. The vapour pressures of the compounds were measured at temperatures between (376.61 and 394.56) K for 9-hydroxy-1, 4-anthraquinone and at temperatures between (363.26 and 386.62) K for 9-methoxy-1, 4-anthraquinone, by the Knudsen-effusion technique. The heat capacity of these two quinones were determined from T = 268.15 K to temperatures near melting with differential scanning calorimetry. From the experimental results, the standard molar enthalpies of combustion, sublimation and formation in the crystalline and gaseous state at T = 298.15 K were derived for 9-hydroxy-1, 4-anthraquinone and 9-methoxy-1, 4-anthraquinone. © 2002 Elsevier Science Ltd. All rights reserved.