In this article, thermosensitive poly(N-isopropyl acrylamide-co-vinyl pyrrolidone)/chitosan [P(NIPAM-co-NVP)/CS] semi-interpenetrating (semi-IPN) hydrogels were prepared by redox-polymerization using N,N-methylenebisacrylamide as crosslinker and ammonium persulfate/N,N,N',N'-tetramethylethylenediamine as initiator. Highly stable and uniformly distributed Ag nanoparticles were prepared by using the semihydrogel networks as templates via in situ reduction of silver nitrate in the presence of sodium borohydride as a reducing agent. Introduction of CS improves the hydrogels swelling ratio (SR) and stabilizes the formed Ag nanoparticles in networks. Scanning electron microscopy and transmission electron microscopy revealed that Ag nanoparticles were well dispersed with diameters of 10 nm. The semi-IPN hydrogel/Ag composites had higher SR and thermal stability than its corresponding semi-IPN hydrogels. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 2690-2697, 2013