PROBLEM TO BE SOLVED: To provide a method for decomposing and removing DNA rapidly without leaking contamination using a high temperature high pressure steam processing unit.SOLUTION: A method for efficiently decomposing and removing DNA without leaking contamination comprises: a process in which an aqueous solution containing a DNA fragment is sealed in a container with air or a gas including oxygen and a process in which the sealed container is placed in an autoclave and held at high temperature so that high temperature high pressure steam process is performed in the sealed container.