PROBLEM TO BE SOLVED: To effectively utilize starch and/or starch inclusion and provide a cheap and useful degradation composition.SOLUTION: A degradation composition is provided by adding starch and/or starch inclusion and water into a cylinder of an extruder, and processing the starch and/or starch inclusion in the cylinder by compressing, mixing, kneading, heating and shearing. A weight average molecular weight of soluble components in the degradation composition is 200,000-5,500,000, and a final viscosity by a viscosity analysis using a rapid visco analyzer with 10% of solid content is 10-200 mPa s.SELECTED DRAWING: None