To develop a simple recovering method of a recombinant protein contained in silkworm silk yarn thereby to solve problems for putting it into practical use in industrial applications.

The recombinant protein produced in silk yarn by a transgenic silkworm is recovered at high purity without a complicated process for protein purification by dissolving the silk yarn in a solution of a neutral salt, an alkaline solution of copper or a urea solution and subsequently dialyzing or diluting with an aqueous solution of a low salt concentration thereby causing the silk yarn protein to precipitate.