A weather strip for a motor vehicle, capable of being readily attached to a flange with a low extensibility, and securely preventing noises from being transmitted via the flange. The weather strip includes a base portion for attachment to the flange, and a seal portion integrally formed with the base portion for sealing between an opening portion and a closing member. The base portion includes at least an outer side wall and a bottom wall, a double-sided adhesive tape is bonded to an interior surface of the outer side wall, and at least one part of the outer side wall and the bottom wall is composed of a hard material such as a hard rubber, which is harder than a material of the remaining part thereof, and a material exhibiting a low extensibility, such as a resin sheet, is stuck to or embedded in the outer side wall and/or the bottom wall.