An opening prevention device for a sliding door which is slidably installed in a side surface of a vehicle is provided. The opening prevention device includes a vehicle movement detection unit that is installed within a vehicle body of the vehicle and is configured to detect movement of the vehicle, and a door opening prevention unit that is installed in the vehicle body and configured to prevent lateral translation of the sliding door when the vehicle movement detection unit detects movement of the vehicle. Additionally, an opening prevention latch is installed on the sliding door to be engageable with a portion of the door opening prevention unit.