[Object] To provide a method of purifying nucleic acids where the operation is simple and the nucleic acids can be extracted in a short time with high efficiency.[Solving Means] A method of purifying nucleic acids including the step of adsorbing substances in a sample containing nucleic acids with an ion exchange resin 10 including a positive ion exchange resin and a negative ion exchange resin. As the positive ion exchange resin, a first positive ion exchange resin and a second positive ion exchange resin having an exclusion limit molecular weight lower than that of the first positive ion exchange resin may be used.