Nanosilver/poly(2-acrylamido-2-methylpropanesulfonate sodium) (nano-Ag/PAMPS) composites were synthesized by a microwave synthesis method. The mechanism of catalytic reduction of Ag ion by atomic nitrogen (from PAMPS) was explored. The composites were characterized by the ultraviolet–visible spectroscopy, x-ray diffractometry, transmission electron microscopy, x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and thermogravimetric analysis (TGA). The results show that Ag nanoparticles (AgNPs) possessed face-centered cubic structure and they were homogeneously dispersed in PAMPS matrix. XPS analysis reveals the interaction between AgNPs and PAMPS matrix. TGA proves that the thermal stability of the pure PAMPS was higher than that of the nano-Ag/PAMPS composites.