A waterproof connector structure comprising: a pair of a male connector housing and a female connector housing fittable to each other, the male connector housing and the female connector housing being capable of preventing water from entering terminal receiving chambers (29, 69) of the connector housings (17, 19) through an opening part of the male connector housing and an opening part of the female connector housing, the opening parts (47, 77) being on a front side of the respective terminal receiving chambers (29, 69) of the connector housings (17, 19) in a fitting direction at a time of fitting the pair of connector housings (17, 19), wherein the male connector housing and the female connector housing comprise a male side cylindrical body and a female side cylindrical body, respectively, in which a front side in the fitting direction is opened, each of the male side cylindrical body and the female side cylindrical body surrounding the respective opening parts (47, 77),the male side cylindrical body and the female side cylindrical body being configured such that an opening end portion of the female side cylindrical body is inserted into an opening end portion of the male side cylindrical body at the time of fitting the pair of connector housings (17, 19), wherein, in the male connector housing, a cylindrical base part in which the terminal receiving chamber which receives a male terminal is formed, a wire holding part which protrudes from the base part to the rear side, and a hood part which protrudes from the base part to the front side are formed integrally, wherein the male side cylindrical body which protrudes from the periphery of the opening part of the base part to the front side to surround the opening part is formed integrally in the hood part, and wherein the female side cylindrical body comprises a projection part which is provided on the opening end portion of the female side cylindrical body entirely in a circumferential direction to protrude outward from the opening end portion of the female side cylindrical body in a radial direction so as to contact the opening end portion of the male side cylindrical body, the projection part being provided on the front side in the fitting direction from the opening part of the terminal receiving chamber surrounded by the female side cylindrical body, a tip part of the male side cylindrical body is deformed elastically outward in the radial direction by the pressure of the projection part of the female side cylindrical body pressing an inner circumferential surface of the male side cylindrical body over the entire circumference, when the female side cylindrical body is fitted to the male side cylindrical body, the restoring force generated by the tip part of the male side cylindrical body elastically deforming presses the projection part of the female side cylindrical body, thereby making the male side cylindrical body and the female side cylindrical body elastically abut each other over the entire circumference through the projection part to seal the gap between the opening part of the male side cylindrical body and the opening part of the female side cylindrical body watertightly, characterized in that the projection part is provided on the front end side of the female-side cylindrical body from a structural member which is supported in the inner wall of the female-side cylindrical body, the structural member forming the opening of the terminal receiving chamber, the structural member is provided to be continuous to an upper surface of the inner wall of the female-side cylindrical body and is provided between the inner wall surfaces which face each other in a width direction of the female-side cylindrical body.