In present study nano-zirconium oxide (zirconia) particles have been prepared by hydrothermal method. Structural, optical and dielectric properties of zirconia nano particles were investigated as a function of pH. The structural and morphological properties of the samples were investigated at different pH (8, 10 and 12) by X-ray diffraction and transmission electron microscopy. The XRD patterns indicated transformation of monoclinic to cubic with increase of pH. The TEM investigation showed that the particles are uniform. Band gap of zirconia was found to increase with increase in crystallite size. The frequency dependence of dielectric constant and dielectric loss of prepared samples were investigated at room temperature. Our result shows dielectric constant linear dependency with crystallite size. © 2015 Elsevier B.V. All rights reserved.