Treatment of the natural strains of seaweed Eucheuma cottonii of the class Rhodophyceae (red seaweeds) remove impurities and fresh water washing and drying to obtain the product. Further purification may be achieved by washing and drying.Carrageenan consists chiefly of potassium, sodium, magnesium and calcium salts of polysaccharide sulphate esters which, on hydrolysis, yield galactose and 3,6-anhydrogalactose.