Poly(vinyl alcohol)-manganese dioxide (PVA-MnO2) nanocomposites with varying compositions were prepared by introducing different amount of preformed MnO2 nanoparticles (NPs) in aqueous solution of a non-conducting polymer, PVA. The PVA-MnO2 nanocomposite films were then prepared by solution casting. The morphology, structure, and thermal stability of the nanocomposites were determined by scanning electron microscopy, dynamic light scattering (DLS) measurements, reflectance spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, and thermogravimetric analyses. The average size of MnO2 NPs measured by DLS was 58 nm. Composite formation with MnO2 NPs was revealed from FTIR spectra in which the bands of -O-H and C=O vibrations of PVA were found to shift, and the bands were observed to be less intense. PVA-MnO2 nanocomposite films with MnO2 content higher than 1.0 wt% shielded ultraviolet (UV) radiation completely, and PVA-MnO2 nanocomposites thus offer the potential for use as UV-shielding materials.