The measured hardness of single-crystal w-ZnO in (0001) direction is 3.7(0.5), and that of polycrystalline w-ZnO sintered at 4.2 GPa and 1000 K is in the range of 4.0-4.5 GPa. The theoretical hardness of w-ZnO is 4.8 GPa, which is slightly higher than our experimental data, which can be explained on the one hand by the imperfect sintering of w-ZnO grains in polycrystals (confirmed by the tendency of H V to decrease with applied force) and on the other hand by the hardness dependence on the crystallographic orientation. However, well sintered polycrystalline w-ZnO samples show values close to 5 GPa, which is in good agreement with the H V value calculated in the framework of the thermodynamic model of hardness. According to this model, for two compounds of the same chemical composition