Herein, cadmium sulfide (CdS) nanospheres were synthesized using the hydrothermal method and then inserted into a polyvinyl butyral (PVB) matrix at different concentrations (0%, 2%, and 4% wt.) using the solution casting method. This work examines the effects of varying percentages of CdS spheres on the structural characteristics, mechanical properties, surface/volume energy loss functions, dielectric constants, and linear/non-linear optical properties of PVB nanocomposite films. The findings confirmed the successful synthesis of sphere-like CdS with a cubic structural phase. The stress-strain curves of PVB and its composites with nano CdS spheres were examined. The PVB has a direct/indirect energy gap of 5.1 eV (4.1 eV). With a CdS doping level of 2% and 4%, the values correspondingly decreased to 4.76 eV (3.36 eV) and 4.49 eV (2.45 eV). The EU values for PVB, PVB-2 wt.% CdS, and PVB-4 wt.% CdS nanocomposite are 15.3, 11.2, and 14.1 meV, respectively. CdS nanospheres decreased the volume and surface energy losses (VELF & SELF) of PVB films. The research demonstrates that the mechanical properties and optical parameters of PVB/CdS nanocomposite films positively correlate with the concentration of CdS nanospheres. These attributes make them well-suited for incorporation into flexible electronic devices.