Middlesex 4 was an English level 13 Rugby Union league with teams from north-west London taking part.

The division was cancelled in at the end of the 1995–96 campaign after nine seasons due to the merger of the Hertfordshire and Middlesex regional leagues.

When the division was created in 1988 it contained the following teams: The original Middlesex 4 was a tier 11 league.

The creation of Herts/Middlesex at the beginning of the 1992–93 season meant that Middlesex 4 dropped to become a tier 12 league.

The introduction of National 5 South for the 1993–94 season meant that Middlesex 4 dropped another level to become a tier 13 league for the years that National 5 South was active.