To provide a cover structure for a slide door capable of surely preventing an arm cover from being removed from a cover position covering a clearance between a door and a vehicle body outer side wall from a front side at full-open of the slide door and attaining enhancement of safety.

The cover structure for the slide door includes a door opening/closing device for moving the slide door 4 for opening/closing a door opening between a closure position D, a projection position D2 on an outer side in a vehicle width direction than the closure position D and a full-open position D3 on the vehicle rear side or a front side than the projection position; a side cover 75 pivotally supported on the vehicle body swingably around a vertical central line Lh, and swinging between the covering position K2 for covering a clearance of an inner wall reached to the projection position and the full-open position and an outer side wall of the vehicle body from a side, and an overlapped position K1 overlapped so as to be laid on the inner wall of the door reached to the closure position D1, and resiliently turned/urged to the covering position; and a turning restriction member 56 projectedly provided on the inner wall of the door 4 so as to block the side cover 75 reached to the covering position from being swung to the overlapped position.