A transfer system for diagnosing a vehicle is provided. The system includes a conveyor that moves the vehicle and a transfer unit that is disposed an input or an output side of the conveyor to move the vehicle into a diagnosing region for vehicle diagnosis. The transfer unit includes a guide rail disposed in both sides of the diagnosing region and a moving body disposed along the guide rail. Swing arms are rotatably connected with a forward and a rear side of the moving body and are concentrated inward to be disposed forward and rearward of a lower portion of a tire. Free rollers are rotatably disposed at each swing arm concentrated inward to clamp the tire. A swing arm driving unit provides a driving force so that the swing arms are concentrated inward or unfolded outward. A moving body moving unit moves the moving body along the guide rail.