The CdS/Epoxy nanocomposites (5%,20% CdS ratio) were prepared by in situ method using cadmium acetate and thiourea as a source of Cd2+ and S2- ions to form CdS nanoparticles in epoxy matrix solution. The X-ray diffraction patterns show that crystallinity of the samples was decreased with increase in the CdS ratio in the nanocomposites. The FTIR and the UV-Visible absorption spectra were performed for prepared samples to determine the assignment bands and the absorption edges respectively. The effective mass model has been used to calculate the diameters of the CdS nanoparticles and they were 4.5 and 4.8 nm for 5% and 20% CdS+ Epoxy respectively. The photoluminescence spectra of CdS/Epoxy showed two emission peaks, the first one varies from 470 to 480 nm for 5% and 20% CdS+ Epoxy respectively, due to energy gap variation with particle size, and the second one at 600 nm bears the signature of the red emission (Lambe_Klick model) which could be due to the recombination of electrons trapped at sulfur (S) vacancies with valence-band-free holes.