The popular Mercedes O302 coach was further developed and modernized and became the O303, presented in 1974. It was available in different lengths, indicated by the number of seat rows (9 to 15) and in different heights, door layouts and seating arrangements. These were indivated by suffix letters, in which R stood for coach (Reise), HD for High Decker, U for regional bus (Uberland), etc. For example a O303-15RHD would be a 12 meter high deck coach, nominally with 15 seat rows. While there were variations in length and height, the coach construction was again highly standardized and as usual Mercedes left the construction of special models such as double deckers and coaches with an undefloor driver position to specialized coach builders. The O303 underframe was again delivered with the front end, so coaches with foreign bodywork would be recognizable as Mercedes. One important market for the Mercedes O303 was Israel, where many received bodywork by Merkavim and Haargaz.
A total of over 37,000 O303 was produced from 1974 until 1991, when it was replaced by the new O404.