There is provided a weather strip for use on a sunroof which can be firmly built in a seal holder even if there occur variations in molding dimensions. The weather strip comprises a thicker base part which is engaged in a built-in recess of the seal holder fixed to a roof glass, a hollow seal part which elastically contacts a roof panel, and a thinner barrel part which is integrally formed between the thicker base part and the hollow seal part and is clamped by an upper protrusion part and a lower protrusion part which are formed in the built-in recess to protrude therein, wherein a continuous angle between an upper surface of the thinner barrel part and the hollow seal part and that between a lower surface of the thinner barrel part and the hollow seal part are set 90° respectively, and an ascent slope is formed on the upper surface of the thinner barrel part and ascends aslant from the hollow seal part toward the thicker base part, and a descent slope is formed on the lower surface of the thinner barrel part and descends aslant from the hollow seal part toward the thicker base part.