Diallyl dimethyl ammonium chloride (DADMAC)-N-vinyl 2-pyrrolidinone (NVP) copolymers were demonstrated to provide excellent stabilities for in situ generated CdS nanoparticles in aqueous medium. Nearly transparent and stable CdS dispersions (up to 0.1 M concentrations) were produced in 1% copolymer solutions. Experiments showed that, increasing DADMAC content induces greater stabilization. UV-visible spectroscopy, fluorescence spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for characterization of the stable nanoparticles. TEM images showed snake-like alignment of nonspherical CdS nanoparticles with 50-70 nm of size, due to template effect of the cationically charged polymer.