To an organic substance having a double bond such as a polyunsaturated fatty acid was added an antioxidative component containing an antioxidative sesame component and ascorbic acid or an ascorbyl fatty acid ester.The above method provides a composition containing an organic substance having a double bond exhibiting enhanced oxidative stability. Particularly, it extremely improves oxidative stability of fat and oil which contains polyunsaturated fatty acid. General-purpose refined fish oil which is easy to handle can be provided for food, medicine or feed uses.
