A connector has a housing with a fit-on tube that can fit in a hood of a mating connector. Terminal fittings are fixed to ends of wires and are held by the housing. A sealing ring is mounted on an annular holding groove on a peripheral surface of the fit-on tube and is disposed between the peripheral surface of the fit-on tube and an inner surface of the hood to seal a gap therebetween. Engaging grooves are formed in the peripheral surface of the fit-on tube. The engaging grooves intersect the annular holding groove and are deeper than a bottom surface of the annular holding groove. Rotation-stopping projections project from the sealing ring to extend along a direction in which the engaging grooves extend and each has an engaging claw that can fit on a bottom of one of the engaging grooves.