<p>Herein, the influence of CeO₂ nanoparticles (NPs) with different concentrations (0, 1, 2, and 3 wt.%) on structural, dielectric constants, and optical properties of PS/CeO₂ nanocomposites was investigated. XRD, SEM, EDX, and mapping images were used to characterize CeO₂ NPs. The crystallite size of the CeO₂ NPs has been found to be 27.31 nm. Additionally, the direct optical bandgap for PS/CeO₂ nanocomposites diminished as the CeO₂ content improved (4.00 -2.91 eV). At the same time, the Urbach energy (Eu) for PS/CeO₂ nanocomposites varied between 1.25 eV and 2.77 eV. The determined single-oscillator energy E_o (4.15 – 3.45&#xa0;eV) and the dispersion energy E_d (0.95 – 3.84&#xa0;eV) as function of CeO₂ NPs were studied. The static dielectric constant (ε_s) and static refractive index (n₀) as the CeO₂ NPs concentration boosts (n₀ from 1.11 to 1.45, ε_s from 1.22 to 2.11) for PS/CeO₂-ii. The ωp value varied from 1.58 × 10¹³ to 4.58 × 10¹³ Hz as the concentration of CeO₂ increases, then reduces to 1.48 × 10¹³ of PS/CeO₂-iii. Also, the high-frequency dielectric constant varied from 1.09 to 1.41 as the concentration of CeO₂ increases. The ratio of the concentration of free carrier ions to the effective mass (N/m*) escalates from 5.44 × 10³⁹ kg⁻¹ m⁻³ for pure PS film to 5.53 × 10³⁹, 15.75 × 10³⁹, and 5.09 × 10³⁹ kg⁻¹ m⁻³ for PS/CeO₂ -i, PS/CeO₂ -ii, and PS/CeO₂ -iii films, respectively. The values of n_∞ and S₀ for PS were found to be 1.10, 2.1 × 10^–6 (nm)⁻², respectively. After adding CeO₂ NPs, the n_∞ and S₀ enhanced for PS/CeO₂-ii nanocomposite and then decreased in PS/CeO₂-iii nanocomposite. Where those values reached 1.47 and 10.60 × 10^–67 (nm)⁻², respectively, for PS/CeO₂-iii nanocomposite. As the concentration of CeO₂ NPs increased, the values of VELF and SELF declined. The structural and optical properties of PS/CeO₂ nanocomposites make them suitable for optoelectronics applications.</p>