A weather strip includes a trim body having a generally U-shaped cross section, a hollow seal portion that protrudes from an outside surface of the trim body, and a holding lip formed on the trim body so as to extend from an inside surface of the trim body toward the inside of the trim body. The weather strip is mounted on the vehicle body such that the trim body is held by a flange provided at a periphery of a door opening of a motor vehicle. The weather strip is formed by extrusion molding such that the length of the holding lip is changed in a stepped manner in accordance with the thickness of the flange.