A mounting assembly for mounting a diesel oxidation catalyst (DOC) system within a work vehicle may generally include a support bracket having a first side and a second side. The mounting assembly may also include a mount plate configured to be coupled to the first side of the bracket. The mount plate may include first and second plate walls and may define an elongated slot through the first plate wall. Additionally, the assembly may include a retention band configured to at least partially wrap around a housing of the DOC system between a first end configured to be coupled to the mount plate and a second end configured to be coupled to the second side of the support bracket. The mount plate may be configured to be moved laterally relative to the support bracket to allow the retention band to be tightened and loosened around the housing.