Nanocomposites of ethylene-vinyl acetate (EVA) reinforced with different quantities of cadmium selenide/cadmium sulfide nanorods (CdSe/CdS NRs) were synthesized by casting method. As confirmed by the energy-dispersive X-ray (EDX) technique, the weight percentages of Cd, S, and Se increased proportionally with NRs, ranging from 0.1 to 0.5 wt.%. XRD data shows that the nanocomposite with 0.2 wt.% of NRs has the highest crystallinity of other studied samples. Scanning electron microscopy (SEM) images demonstrated that all samples exhibited a uniform, dense structure with non-porous surfaces devoid of cracks or defects. Several optical parameters were calculated, demonstrating their dependence on the NRs content. As the NRs content increased, a decrease in skin depth (δ) was observed (except for 0.2 wt.%), which is attributed to enhanced absorption and reduced transparency. The energy gap was reduced as the concentration of the doped NRs rose. This effect can be ascribed to the defects’ structure in a prepared polymeric matrix, leading to the emergence of localized states inside the transition energy band gap. Then, the Z-scan technology measured the optical nonlinearities with open and closed aperture. It showed that prepared samples have strong nonlinear absorption, and the values of optical nonlinearity parameters of n2 and χ 3 ranged from 1.29 × 10− 13 to 5.46 × 10− 13 cm2 w− 1 and from 3.79 × 10− 12 to 27.6 × 10− 12esu, respectively, with varying the molar ratio of the prepared nanocomposite film. Our study validated that the CdSe/CdS NRs/EVA nanocomposites exhibit exceptional nonlinear optical properties, potentially advancing the field of nonlinear optics.