Graft polymerization of vinyl monomers onto silk were carried out in aqueous medium using ceric salt as an initiator, and discussed about the mechanical properties of silk. The results obtained are summarized as follows: 1. Percent grafting is greatly enhanced by the increasing of the temperature. 2. Effect of percent grafting is in the order of methyl methacrylate, and vinyl acetate. 3. Strength is decreased in the high grafted silk, and elongation is increased in the low grafted silk.