Abstract: An ink, which contains DNA and is hardly decomposed by an external stimulus such as ultraviolet light, heat, an acid or an alkali, is provided. A method of easily analyzing a DNA in an ink composition is also provided. An ink composition containing a DNA and having a water-tolerance at a certain level or higher is prepared. The DNA in a print that is produced by using the above ink composition is quickly extracted with water or an aqueous solution and analyzed. Furthermore, a DNA in a print that is produced by using an oil- and water-based ink composition containing the DNA is quickly extracted with water or an aqueous solution and analyzed.