The present invention is a method for isolating and purifying a nucleic acid, where generation of foams is able to be suppressed whereby the isolation and purification of a nucleic acid are easily and efficiently carried out, the method for isolating and purifying a nucleic acid comprising the step of: (1) contacting a sample solution containing nucleic acid to a solid phase to adsorb the nucleic acid onto the solid phase; (2) contacting a washing solution to the solid phase to wash the solid phase in such a state that the nucleic acid is adsorbed; and (3) contacting an elution solution to the solid phase to desorb the nucleic acid, wherein the sample solution containing nucleic acid contains an antifoaming agent.