The structure and optical properties of polyvinyl alcohol (PVA) – Ni nanocomposite films are investigated by a scanning electron microscope (SEM), X-ray diffractometer (XRD), and UV–Vis spectroscopy. It is confirmed the semi-crystalline nature of PVA films. The degree of crystallinity decreases with the increase in Ni nanoparticle concentration. The surface morphology of polymer films is changed from smooth into rough with the increase in Ni nanoparticle concentration in the polymer matrix. The increase of Ni nanoparticle concentration in the polymer matrix leads to: a decrease in optical band gaps (direct and indirect) and increase in Urbach tail energy, refractive index and extinction coefficient of polymer films. The optical dielectric properties and optical conductivity increase as well, with an increase in Ni nanoparticle concentration. The nonlinear optical properties (third-order nonlinear optical susceptibility and nonlinear refractive index) are calculated using the Wemple–Di Domenico single oscillator model.