A sliding door and a safety device thereof are described. The sliding door is opened and closed parallel to a body of a car to reduce efficiently the width requirement for opening a car door. The sliding door has a door body, a power transmission device, and a supporting device. The supporting device supports the sliding door and couples the power transmission device to the body of the car by way of only one end portion of the door body. The sliding door further has a handle and a safety device to enhance effectively driving safety.