This invention is intended to efficiently extract and purify a target foreign protein expressed with the use of an E. coli strain from the periplasm. This invention provides a method for producing a protein comprising the steps (a) to (c) below: (a) a step of introducing a gene encoding a target foreign protein into E. coli having modification in a gene associated with maintenance of the outer membrane structure; (b) a step of culturing the E. coli of (a); and (c) a step of recovering a target foreign protein from the periplasmic fraction of the microbial cell after culture.