The crystal phase and shape of ZrO₂ nanoparticles were finely tuned by mediating the hydrolysis rate of zirconium cations and using sodium oleate as the capping agent under hydrothermal conditions. Pure monoclinic ZrO₂ nanorods with a diameter of ~3 nm and length of 30–40 nm were obtained at a lower pH value of 9.4; whereas monodispersed ZrO₂ particles of ~4 nm with mixed monoclinic and tetragonal phases were formed at a higher pH value of 11.4. Their formation mechanism was discussed in terms of the hydrolysis rate of the zirconium cations and the structure-directing role of the oleate species. The monoclinic ZrO₂ nanorods showed prominent blue-green fluorescence under excitation by an ultraviolet lamp (365 nm) because of the presence of a large number of oxygen-vacancy defects.