A gasket for a door mirror according to the present invention is constructed so that when the gasket is interposed and pressed between a mirror base of a door mirror and a mounting seat of a car body, a tip part of a seal lip is pushed against a seating surface of the mounting seat, so as to tilt and bow toward a circumferential portion of the gasket. Then the tip part of the seal lip is resiliently urged against the seating surface of the mounting seat because of its flexibility, so as to seal a clearance between a joint surface of the gasket and the mounting seat of the car body throughout the entire circumference.