Methods of using OmpT protease are provided. In particular, the invention provides for a method of controlling cleavage of a polypeptide by OmpT protease comprising, converting a sequence site comprising two arbitrary consecutive amino acids and/or amino acid(s) in the vicinity of the site in the polypeptide into other amino acids; which method comprises setting lysine or arginine as the amino acid at the -1-position concerning the site and setting a specific amino acid as the amino acid at the +1-position; and/or setting specific amino acid(s) as the amino acid(s) at the -4-position and/or the -6-position relative to the site; so that a desired part of the polypeptide is cleaved by OmpT protease and/or an undesired part of the polypeptide is not (or hardly) cleaved by OmpT protease. A method of producing a target polypeptide is also provided.