A sliding door structure of a vehicle is provided for sliding a door body with respect to an opening portion of a vehicle body in forward and rearward directions of the vehicle body for opening and closing. The sliding door structure includes a rail disposed on the door body and aligned with the forward and rearward directions of the vehicle body. An arm protrudes from an edge portion on a door opening direction side of the opening portion of the vehicle body, and is configured to engage with the rail to hold the door body movably in the forward and rearward directions. The door body is able to slide in the door opening direction after engagement between the vehicle body side engagement portion and the arm side engagement portion when the arm pushes the door body outwardly in the width direction of the vehicle.