The fabrication of nanocomposites by covalent inclusion of inorganic nanoparticles in an organic polymer matrix is highly topical and may find applications in the electronics, optics and energy sectors. Incorporation of CdS nanoparticles into the polyacrylonitrile (PAN) matrices could be expected to display improved or enhanced optoelectronic and optical properties. Using a newly synthesized RAFT agent, i.e., CdS-DDAT nanoparticles (DDAT: S-1-Dodecyl-S0-(a, a0-dimethyl-a00-acetic acid) trithiocarbonate), CdS covalently functionalized polyacrylonitrile (CdS-PAN) nanocomposite material was prepared in the presence of small amount of AIBN under ultrasonic radiation. This material, which exhibits an induced positive nonlinear absorption of incident light, has been well-characterized by a variety of physical techniques such as GPC, UV/vis, FT-IR, TGA, XRD and Z-scan.