Abstract: A DNA encoding 20K hGH is connected directly to a gene encoding Escherichia coli OppA protein secretion signal, or a modified form thereof, and a DNA encoding signal peptidase 1 to construct a recombinant plasmid, E. coli is transformed by said plasmid and cells of the resulting E. coli transformant strain are cultured for secretory production of the 20K hGH in the E. coli periplasm. This method enables efficient secretory production of 20K hGH and easy isolation and purification of 20K hGH from the periplasm fraction because the level of impure proteins in the E. coli periplasm is low.