Disclosed is a process for separating and/or purifying a nucleic acid by elution of the nucleic acid from anion exchange resins under conditions of high salt concentration and the presence in the eluant of an additive comprising guanidine, or a guanidine-like derivative. The process allows high recovery of nucleic acids from anion exchange resins without impairing the nucleic acid stability as compared with conventional ion exchange chromatographic procedures.