A connector housing with a mat seal, includes a connector housing a mat seal. At an outer surface of a rear wall of the connector housing, a plurality of passages for a silicone gum forming material are provided outside an area where a plurality of terminal insertion holes are formed. On the outer surface of the rear wall and outside the passages, an annular rib is protruded and surrounds an area inside the annular rib. The mat seal is molded by using the area inside the annular rib as a reservoir space in which the silicone gum forming material overflowing from the seal forming cavity is retained, and using at least one of the passages as a passage for a gate through which the silicone gum forming material is injected into the seal forming cavity, and the other of the passages as passages for overflow.