A method for separating and purifying RNA including the steps of passing a sample solution containing a nucleic acid, a washing solution and a recovering solution through a nucleic acid-adsorbing porous membrane to adsorb nucleic, adsorbing, washing and recovering, in which the nucleic acid adsorbing porous membrane is a porous membrane capable of adsorbing a nucleic acid by interaction involving substantially no ionic bond, and the sample solution is obtained by a process, comprising the steps of (I) injecting a test sample containing at least one of blood and leukocyte, and further containing an anticoagulant to a container, (II) adding a hemolytic agent to the container to obtain a leukocyte pellet, (III) adding a nucleic acid-solubilizing reagent to the leukocyte pallet to obtain a mixture solution and (IV) adding a water-soluble organic solvent to the mixture solution to obtain the sample solution containing the nucleic acid.