A method for selectively separating and purifying RNA from a mixture solution of nucleic acid containing DNA and RNA, wherein the method comprising the steps of: (1-a) adsorbing nucleic acid; (1-b) washing; (1-c) subjecting to a DNase treatment; (1-d) washing; and (1-e) desorbing the RNA from a nucleic acid-adsorbing porous membrane by a recovering solution, wherein in the step (1-c), a total amount of a DNase solution is 130 μl or less per 1 cm2 of the membrane. And a method for selectively separating and purifying RNA or DNA, which comprises the steps of: (2-a) adsorbing nucleic acid; (2-b) washing by a washing solution; and (2-c) desorbing the nucleic acid from a nucleic acid-adsorbing porous membrane, wherein the washing solution contains a water-soluble organic solvent having a concentration of 50% by weight or less, and does not contain a chaotropic salt.