A weather strip has a trim part adapted to be mounted on a flange, a seal part having a hollow portion and a cover lip. The trim part has a bottom wall portion, and an interior and an exterior side wall portions which constitute a pair of side wall portions and is formed into a shape, as a whole, having a substantially U-shaped cross section, and an insert of a center bonded type is embedded in the interior of the trim part so constructed. In a skeletal piece of the insert, an angle .theta.a formed by a bottom wall part embedded in the bottom wall portion and an internal part embedded in the interior side wall portion and an angle .theta.b formed by the bottom wall part and an external part embedded in the exterior side wall portion are made to form acute angles.