Nanocomposite films of polyaniline protonated with camphor sulfonic acid (PANI-CSA) hosted in polyethylene oxide (PEO) and incorporated with gallium nitride nanoparticles (GaN-NPs) were synthesized and characterized. Nanocomposite films were coated on activated fused silica substrates by employing the spin coating technique. Films of PANI-CSA, PEO, PANI-CSA-PEO, and PANI-CSA-PEO incorporated with GaN-NPs with a weight percent ratio of 10%, 20.07%, 38.76%, 77.83%, 93.03%, 100.78%, and 155.04% with respect to PANI-CSA were characterized using UV–Vis spectroscopy, XRD, and SEM. Refractive index ( n ), extinction coefficient ( k ), absorption coefficient (α), and bandgap energies ( E g ) were deduced. The refractive index value of PANI-CSA-PEO at 550 nm is found to be 1.72. It increases to 1.82 when GaN-NPs have been added to PANI-CSA-PEO solution by 10 wt.%. Then, it decreased to 1.63 when GaN-NPs concentration was increased to 20.07 wt.%. When GaN-NPs is increased further to higher concentrations, the material becomes GaN-rich PANI-CSA-PEO, and the refractive index takes values ranging between 1.56 and 1.66 at the higher concentration. The typical crystalline structure of PANI-CSA was vanishing gradually as GaN-NPs content was increasing at 155% wt.%, and the GaN crystalline nature was dominating the film crystallography. Results are anticipated to contribute to preparing smart multifunctional devices based on the PANI-CSA-PEO doped with GaN-NPs.