The Metropolitan Borough of St Marylebone was a metropolitan borough of the County of London from 1899 until in 1965 it was amalgamated with the Metropolitan Borough of Paddington and the Metropolitan Borough of Westminster to form the London Borough of Westminster.

It was that part of the current London Borough which is north of Oxford Street, and east of Maida Vale and Edgware Road. It included the areas Marylebone, Regent's Park, St John's Wood, and Lisson Grove. It has Marylebone railway station.

See also: London, United Kingdom