Abstarct: In this work pure and Ca doped CeO2 thin films were prepared by sol-gel method. The effects of deposition technique, drying treatment, substrate type, annealing treatment and Ca doping on the structural and optical properties of CeO2 thin films were investigated. For characterization of the samples, different measurements have been employed. X-ray diffractometry (XRD) and scaning electron microscopy (SEM) respectively were used to identify the structural of the samples; transmittance and reflectance measurements were used to determine the variation optical parameters. Our results showed that the samples were deposited by spin coating techniqe are smoother and thinner compared to dip coated samples. The films dried at temperature 100℃ have higher optical transmittance. The samples which deposited on glass substrate were thinner than the samples deposited on quartz substrate. XRD patterns showed that the crystallinity of the samples was improved by annealing treatment in the selected temperature range (300℃, 400℃, 500℃). Annealing treatment eliminated oscillatory nature of the transmission and reflectance spectra and decreased the band gap energy; and also absorption edge significantly shifted to larger energy (red shift). The XRD spectra of the films with 2, 5, 15, 20 (%Wt) of Ca indicated that these films have Flurite cubice structure and grain size of the samples decreased with increasing of Ca doping. The results also showed that the bandgap energy increased with increasing of Ca doping.