Zirconia nanorods and nanoparticles were grown hydrothermally starting from zirconium monoxide powder. The process was performed in an autoclave using NaOH as a mineralizer at nominal concentrations 15M, 20M and 25M, and at a temperature of 200°C for 1week. The samples were characterized by high resolution transmission electron microscopy, showing that the nanorod diameter spanned from 25 to 200nm and their length from a few hundred nm up to 2μm. X-ray photoelectron spectrometry showed that after the treatment all the material was zirconium (IV) oxide, as confirmed by X-ray diffraction and selected area electron diffraction. The latter showed that the nanobars were in the monoclinic phase and the nanopowders in the tetragonal one.