This paper shows the ex situ thermal treatment effects of the ZrO2 thin films obtained by TVA (thermionic vacuum arc) technique on the optical properties (e.g., transmittance, refractive index and band-gap energy) of ZrO2 thin films. The crystal structure, surface and optical properties were investigated for ZrO2 thin films deposited on glass substrates by thermionic vacuum arc (TVA) method. The thermal treatment effect on the optical properties of the thin films was determined. The XRD analysis showed that the deposited ZrO2 thin films have baddeleyite (monoclinic) and zirconium (hexagonal) structures. The thicknesses and refractive index were determined by interferometric measurements. The thin films were thermal treated at different temperatures (350 degrees C, 450 degrees C and 550 degrees C), and the analysis showed that the optical properties of ZrO2 deposited thin films were improved by thermal treatment at 450 degrees C. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.