Poly(styrene) was grafted onto silk fibers in an aqueous medium, using ammonium persulphate initiator. Add-ons of up to 100% were achieved. The add-on increased linearly with the monomer concentration of the grafting system, all other factors remaining constant. The yield of the reaction attained about 80% and the extent of homopolymerization was negligible. The equilibrium moisture regain decreased noticeably with increasing add-on. Breaking load showed a tendency to increase in the 0-55% range of poly(St) content, while elongation at break and work of rupture decreased. The DSC endothermal peak at 315 degrees C slightly shifted towards higher temperature by graft-copolymerization, and a new endothermal transition appeared beyond 400 degrees C. TG measurements showed an increase of weight retention beyond 300 degrees C for poly(St)-"grafted’ silk fibers. The dynamic mechanical behavior was characterized by a shift to lower temperature of the loss modulus peak. The transverse dimension of the fibers increased with increasing add-on. The polymeric residue remaining after alkaline dissolution of silk fibroin showed a porous texture with a sponge-like morphology. The molecular weight of poly(St) removed from silk increased up to 120 kDa in the 0-55% add on range and then remained constant. The "Poly(St)/Silk" molar ratio increased linearly over the add-on range examined.