The advancement in cost-effective techniques for the growth of high-quality NiO thin films are an instrumental for design and fabrication of NiO film based nano-devices, especially solar cells, light emitting diode, lasers etc.  In this study, it has been demonstrated that the optical, electrical and structural properties of NiO thin films onto glass substrate deposited using low cost sol-gel method is strongly influenced by post thermal annealing treatments in ambient air. As-deposited NiO thin films were analyzed in details. The X-ray diffraction (XRD) measurements indicate the enhancement of the crystal quality of films after annealing. The optical performance of NiO thin films were enhanced after being thermal annealed at 300 °C and 600 °C as a result of improvement in the density of states. Also, raise in annealing temperature affected band gap energy to decrease from 3.63 eV to 3.44 eV and resistivity values of the NiO films were changed between 1020 ohm-cm and 700 ohm-cm. Further, results suggest that the cost-effective sol-gel deposition technique have a greater potential to be used for the development of high-quality improved p-type NiO films with minimum defects for electronic device applications.