Polyacrylonitrile (PAN)/silver (Ag) nanoparticle composites were in-situ synthesized by ultraviolet irradiation of a mixture of silver nitrate (AgNO3) and acrylonitrile (AN) monomers. The resultant composites were characterized by infrared spectroscopy (IR), X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (TEM). It was found that polymerization of AN monomers and reduction of silver ions occurred simultaneously, thereby leading to the formation of the PAN/Ag composites. TEM image revealed that silver nanoparticles with a diameter ranging from 5 to 10 nm were well dispersed in PAN matrix. It was found from the reaction mechanism that the complex of silver ions with AN monomers provided an excellent precursor for this synthesis, which is responsible for homogeneous dispersion and narrow size distribution of silver nanoparticles.