The Vickers hardness (H V ) of bulk single-phase nanocrystalline rs-ZnO (sample #1) is 7.0(15) GPa, while hardness of rs-ZnO synthesized from the solution-chemistry w-ZnO nanoparticles (quenched from 7.7 GPa and ~800 K) is ~5.5(1.0) GPa (Fig. ). The observed improvement of mechanical properties (over 25% in the case of H V ) is apparently due to the better sintering of the nanoparticles.