An object of the present invention is to provide a method for identifying a physiologically active protein translated from an ORF other than mORF present on mRNA.The object can be solved by a method for identifying a physiologically active protein, wherein an ORF which encodes a protein having a physiological activity, other than a main open reading frame (ORF) is identified in eukaryotic mRNA, comprising the steps of: (1) introducing an expression vector incorporating a candidate ORF to cells, and culturing the introduced cells, (2) detecting a protein bound to a candidate protein by immunoprecipitating the candidate protein translated from the candidate ORF, from the cultured cells, (3) determining a candidate protein in which another protein bound to the candidate protein is detected as a physiologically active protein.