PURPOSE: To obtain high-quality silk yarn by treating waste cocoons with a special chemical, putting the resultant cocoons to high-temperature and high-pressure treatment followed by cooling, washing with water and drying followed by making the cocoons into a cotton-like form which is then spun into silk yarn.

CONSTITUTION: Waste cocoons after collecting raw silk are impregnated, at normal temperature and pressure, with a chemical comprising (A) an admixture made up of (1) 16wt. of a nonionic surfactant, (2) 14wt.% of a quaternary ammonium-type cationic surfactant, (3) 6wt.% of a cationic soap, (4) 5wt.% of a neutral detergent, (5) 3wt.% of castor oil, (6) 2wt.% of sodium silicate, (7) 2wt.% of dilute sulfuric acid, and (8) 2wt.% of a catalyst, and (B) an equal amount of water, and held for ca.24hr. Thence, the resultant system is subjected to a pressure of ca.150 1b and temperature of ca.100°C in an autoclave and then left to stand for 90-100min. until normal temperature and pressure are reached. The resulting waste cocoons are washed with water and dried to a moisture content of ca.13wt.% followed by forming said cocoons into a cotton-like form using a silk-opening machine and then spinning silk yarn from the cotton-like form using a spinning machine. This spinning is made within 12hr after the water washing.