In the present work, HfO2 thin film (100 nm) has been deposited by sputtering technique and annealed at various temperatures ranging from 400 to 1000 °C (in step of 200 °C) in O2 ambient for 10 min. The samples have been characterized using XRD, FTIR, EDAX, AFM and Laser Ellipsometer. The impact of annealing temperatures in O2 ambient on structural properties such as crystallite size, phase, orientation, stress have been studied using XRD. The Hf–O phonon peaks in the infrared absorption spectrum are detected at 512, 412 cm−1. The stretching vibration modes at 720 and 748 cm−1 correspond to HfO2. AFM data show mean grain size in the range of 38–67 nm. The film reveals variation in structural properties, which appears to be responsible for variation in oxygen percentage, refractive index (1.96–2.01) at 632 nm wavelength and roughness (6.13–16.40 nm). Annealing temperature as well as ambient condition has significant effects on stress, crystal size and thus the arrangement of atoms. For good quality film, annealing temperature larger than 600 °C is desired. © 2016, Springer Science+Business Media New York.