The flag of Middlesex is the flag of the English county of Middlesex. This is the traditional flag of Middlesex, the county that forms the central and north-west parts of Greater London. This traditional design is included in the Flag Institute's registry of local flags as the Middlesex Flag.
The flag is a banner of the arms of the former Middlesex County Council, abolished in 1965. Whilst such banners of county arms are legally not generally available for public use, a similar design had been used traditionally as a local badge in Middlesex and neighbouring Essex for centuries.