A flavor improver for a polyunsaturated fatty acid-containing fat or oil, containing a basic peptide; and a polyunsaturated fatty acid-containing fat or oil composition, containing a fat or oil containing a polyunsaturated fatty acid having 18 or more carbon atoms and two more double bonds, a basic amino acid and/or a basic peptide, and an emulsifying agent. The flavor improver for a polyunsaturated fatty acid-containing fat or oil and the polyunsaturated fatty acid-containing fat or oil composition of the present invention can suppress the generation of unpleasant taste and flavor from the polyunsaturated fatty acid over a long time period.