PURPOSE:To dye silk in noble and deep color without color change nor color failure even held in bright place for a long time by treating silk with noble metal salt and developing color by treating with reducing agent. CONSTITUTION:Silk is subjected to dipping treatment in aqueous solution of noble metal salt (e.g., chloroauric acid, palladium chloride or chloroplatinic acid) of preferably 1-100mmol/l concentration at 0-100 deg.C for 10sec-10 hour and treated with reducing agent (e.g., sodium boron hydride) to color brown, gray, violet, yellowish brown or dark brown, etc.