A foldable seat mounting rack of a foldable motorized vehicle includes a pair of symmetric foldable seat mounting support. Each symmetric foldable seat mounting supports comprises: an upper mounting base, a lower mounting base, a pinion, a locking lever, a main connecting plate, a first and a second auxiliary connecting plates. The main connecting plate is pivoted on both upper and lower mounting bases. The pinion is pivoted at a middle portion on an inner side of the main connecting plate. Side surfaces at one end of the both auxiliary connecting plates are formed with racks engaging with the pinion. The first auxiliary connecting plate is pivoted on the lower mounting base and the second auxiliary connecting plate is pivoted on the upper mounting base. One end of the locking lever is pivoted on the upper end of the main connecting plate, and the other end presses against the pinion.