Hybrid composites of PbS nanoparticles embedded in sulfonated polystyrene matrixes were prepared without other added capping agent in the random ionomer. The nanocomposites were found to exhibit photoluminescence in both the near-infrared and visible regions. The infrared luminescence was tunable in the range 1100-1500 nm via quantum size effect. XRD, TEM, UV-vis, FTIR, DSC, and XPS techniques were employed to investigate the size, shape, morphology, absorption, and thermal properties as well as the formation mechanism of nanoparticles in the ionomer matrix. The unique microstructure of the sulfonated polystyrene ionomer was found to provide a confined medium for the formation of nanoparticles. The -SO 3groups acted as the coordination sites for Pb 2+ ion aggregation, PbS nanoparticles were then successfully grown in situ at these sites with a supply of S 2from thioacetamide. The sizes and shapes of the PbS nanoparticles produced were controllable by varying the sulfonate content of the polymer and the initial feed concentration of Pb 2+ ions. The average size of PbS nanoparticles was estimated to be 5-8 nm, with size dispersity of ∼10-12%. Some PbS nanorods, with an average diameter of 3.5 nm, were formed at higher Pb/SO 3 H feed ratios.