A vehicular vision system includes an electronic control unit (ECU) disposed at a vehicle and including an image processor that processes image data captured by at least one camera of the vehicle. An under-trailer camera is disposed at an underside of a trailer hitched to the vehicle. The under-trailer camera has a field of view under the trailer that includes a ground surface under the trailer that is traveled over by the trailer. The under-trailer camera captures image data as the vehicle and trailer are moving. The ECU, responsive to processing of image data captured by the under-trailer camera, detects an object under the trailer and determines that the detected object under the trailer is greater than a threshold size. The ECU, responsive to determination that the detected object under the trailer is greater than the threshold size, generates an output.