The Mercedes-Benz O303 was a model of coach produced by Mercedes-Benz between 1974 and 1992. The design was very successful, with 33,000 being sold, including 222 in the United Kingdom. It replaced the O302 and was replaced by the O404.

Many models of the O303 were produced, including the O303, O303/15R, O303/15RHD, O303/15RHP, O303/15UE, and O303/15UP. The majority of O303s sold were of the standard O303/15R variety. In 1985, the O303 was the first bus to offer anti-lock braking systems (ABS).

Three O303/15UP "Jumbulance" buses were built to replace the previous O302/13R. All were delivered to Across Trust of Morden, who were also the only customer for the O302 version of the Jumbulance.

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