A refolding agent and refolding method which makes it possible to produce high-purity proteins in high productivity. The refolding agent includes a phosphorus-containing compound (A) and an oxycarbonyl group-containing compound (B). The refolding method includes the step of treating the unfolded protein with the refolding agent. As the compound (A), there may be at least one selected from inorganic phosphoric acids, alkyl phosphate esters, sugar phosphate esters, and salts of these, and as the compound (B), there may be at least one selected from formic acid, acetic acid, propionic acid, lactic acid, tartaric acid, and salts of these.