To provide an anti-swing structure for a top-railed sliding door, which positively constrains both lower ends of the sliding door in a traveling direction even when the top-railed sliding door is closed, and can efficiently prevent swinging and looseness of the sliding door in a width direction.

The anti-swing structure is arranged at a butt portion between a butt end face of the top-railed sliding door and a rebate vertically carved in a longitudinal frame. The anti-swing structure is constituted of a projecting portion, a lever, and an anti-swing member. The projecting portion moves to and fro by butting on the butt end face of the top-railed sliding door or separation from the same, and by a function of a compression spring. The lever is rockably supported by a pivotal shaft. The anti-swing member is slidably supported by a support member in an axial direction. The anti-swing structure is formed by rotatably pin-connecting the projecting portion and the anti-swing member to both ends of the lever.