Middlesex 3 was an English level 12 Rugby Union league with teams from north-west London taking part.

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

When league rugby began in 1987 this division was split into two regional leagues containing the following teams: North South The original Middlesex 3 was a tier 10 league, split into two regional divisions (north and south).

The creation of Herts/Middlesex at the beginning of the 1992–93 season meant that Middlesex 3 dropped to become a tier 11 league.

The introduction of National 5 South for the 1993–94 season meant that Middlesex 3 dropped another level to become a tier 12 league for the years that National 5 South was active.