A weather strip exhibiting excellent sealing properties, of which a tubular seal portion is prevented from readily tilting when attached to a curved flange in a vehicle body. The weather strip includes a trim portion having a generally U-shaped cross-section and a tubular seal portion. The tubular seal portion includes a first outer seal wall, a second outer seal wall, a first inner seal wall, a second inner seal wall, an outer flexing part and an inner flexing part. The thickness of the tubular seal portion decreases in the order of joint areas of the first outer seal wall and the first inner seal wall to the trim portion, the second outer seal wall and the second inner seal wall, and the outer flexing part and the inner flexing part.