A sealing structure for forming a seal between a weather strip attached to a door opening portion of a vehicle body, and a periphery of a vehicle door. The weather strip includes a base portion having a generally U-shaped cross-section for attachment to the door opening portion, and a tubular seal portion which expands from an outer side wall of the base portion. A projection is formed in the weather strip so as to project from the outer side wall of the base portion into an interior of the tubular seal portion so as to be spaced from an inner surface of a projecting top of a sealing wall of the tubular seal portion. When the vehicle door is closed, an inside surface of a periphery of a door panel contacts and presses the projecting top of the sealing wall, which faces the projecting end of the projection, while an inside surface of a door frame contacts and presses a side part of the sealing wall apart from the projecting top of the sealing wall.