The invention provides a steel plate reinforcing sheet having light weight and thin layer, providing sufficient adhesion and reinforcing effect to a steel plate, and having excellent workability. In the steel plate reinforcing sheet comprising a restricting layer and a resin layer, a curing composition is first prepared by mixing rubber components comprising diene-based rubber and rubber having a vinyl group in its side chain, with a cross-linking agent capable of reacting with these rubber components, and then by kneading the mixture. Thereafter, the curing composition thus prepared is rolled by molding, to form a resin layer. Then, the resin layer thus formed is adhesively bonded to the restricting layer, to produce a steel plate reinforcing sheet.