A method for separating components using a supercritical fluid chromatograph, including: injecting a sample into a mobile phase containing a supercritical fluid and a modifier to introduce the sample into a column; and separating components in the sample during passing through the column; wherein the sample contains an oligonucleotide as a target component; the supercritical fluid contains carbon dioxide; and the modifier contains a solution containing at least one selected from the group consisting of ammonium, an alkylamine, and an amino alcohol, and an acid.