​We synthesize and optically characterize pure PMMA and PMMA incorporated with metal oxides nanoparticles (MO NPs) such as ZnO, CuO, TiO₂ and SiO₂ NPs nanocomposite thin films with weight concentration of 10% using dip-coating technique. SEM images of MO NPs show that all NPs have nearly an average size of around 50 nm. The optical parameters such as, optical parameters (n and k), optoelectronics properties, dispersion, band-gap energy and band structure of as-prepared nanocomposite thin films were determined by analyzing the transmittance and reflectance spectra. Mainly, optical band-gap energy (E_g) and the thickness of thin films are evaluated to a high degree of accuracy by utilizing Q-functional derived using a mathematical model recently published. The Q(E) is a functional containing experimental transmission and reflection data and the incident photon energy. The E_g value of un-doped ​