A seat opening concealment structure is provided including a cover member that covers part of a vehicle seat, and that includes an outer wall including a curved face portion with a circular arc shaped cross-section profile, the outer wall being formed with an opening having an elongated profile along a peripheral direction of the curved face portion, and the outer wall being formed with a larger radius of curvature at an inner face of the curved face portion than a radius of curvature at an outer face of the curved face portion. The seat opening concealment structure further includes a rotatable body that is supported via a coupling section inserted through the opening so as to be rotatable relative to the cover member, and a concealing sheet that is provided with an attachment hole at which the coupling section is attached, that is longer than a length of the opening, that is supported at two width direction end portions of the concealing sheet so as to be slidable along the inner face of the outer wall, and that covers the opening.