Provided are a method of isolating a nucleic acid from a sample and a solid material for isolating the nucleic acid which can be used for the above method. The method includes contacting the sample with a bifunctional material containing an amino group and a carboxyl group at a first pH to bind the nucleic acid to the bifunctional material, the bifunctional material being positively charged at the first pH; and releasing the nucleic acid at a second pH which is higher than the first pH.