There is provided a waterproof connector structure which includes a pair of connector housings. An opening end portion of a cylindrical body of one connector housing is inserted into an opening end portion of a cylindrical body of another connector housing at the time of fitting. One cylindrical body has a projection part which is provided to protrude outward in a radial direction from the opening end portion thereof entirely in a circumferential direction. The projection part is provided on a front side in a fitting direction from an opening part of a terminal receiving chamber surrounded by the one cylindrical body.