Abstract: The present invention relates to a method for isolating a nucleic acid by using: a binding buffer containing acetic acid or phosphoric acid; and the pH difference between binding and washing buffers, and an elution buffer, wherein silica magnetic particles are added to a biological sample including a nucleic acid to which a binding buffer containing acetic acid, phosphoric acid, etc., has been added, thereby binding the nucleic acid to the magnetic particles, after which a magnetic field is applied to separate the magnetic particles, and the nucleic acid is purified in a basic pH elution buffer. The method uses the pH difference, and can isolate the nucleic acid more quickly and efficiently than centrifugation or gravity separation. In addition, since ethanol is not used, high-purity nucleic acid can be isolated and purified to obtain more accurate results in subsequent experiments.