We present experimental results on polymer-based nanocomposite made of styrene with butyl methacrylate (SBMA) (1:1) and inorganic semiconductor CdS. Photoluminescent nanocomposites based on styrene with butylmethacrylate copolymer (SBMA) (1:1) and inorganic semiconductor CdS were prepared by simple chemical method using organic solvents instead of water as was described elsewere [1]. Thin film composite samples with calculated content 20% and 40% of CdS have been characterized by UV-Vis absorption and photoluminescent (PL) spectroscopy, as well as by transmission electron microscopy (TEM). PL spectra were measured under excitation of a laser beam 337 or 405 nm using a MDR-23 monochromator and a photon counting module H9319-12 connected to a PC. The composite films with the thickness 5-15 μm were obtained on cleaned glass substrates by a spin coating of copolymer/cadmium nitrate with thiocarbamide solution [1]. Spin-coated films were thermally treated at 80-100 ºC for different time interval for variation of size of CdS nanoparticles. Transmission electron microscope (TEM) examination confirms a relatively narrow distribution of the CdS nanoclusters in the SBMA matrix, which covers the range 2-10 nm (Fig. 1). On the other side, the average CdS particles size estimated from the position of first excitonic peak in the UV-Vis absorption spectrum (Fig. 2), was found to be 2.8 nm and 4.4 nm for two samples with different duration of thermal treatment time, which is in good agreement with PL experimental data (Fig. 3). The small nanoparticle diameter correlates with the strong shift of the PL maximum at 382 nm for sample 1 and 465 nm for sample 2 (fig. 3). FWHM value for the main PL peak slightly varies in the range 40-45 nm. This suggests the size distribution of the nanoparticles around the mean diameter value. The PL spectrum for CdS nanocrystals is dominated by near-band-edge emission. The relatively narrow line width (40-45 nm) of the main PL band (Fig. 3) suggests the nanoparticles having narrow size distribution. On the other side, relatively low PL emission from surface trap states at longer wavelengths were observed in the region 500-750 nm indicating on recombination on defects.