In a waterproof structure for a connector, in order to prevent that water is infiltrated into openings of cavities accommodating terminals, a pair of housings include resin annular members which protrude in a fitting direction to surround the openings. One annular member has a protrusion part which is formed on a way between a tip and a root thereof over an entire circumference. The protrusion part is formed to have a top part which presses an inner circumferential surface or an outer circumferential surface of the counterpart annular member at a time of fitting the pair of housings.