The 1985–86 season was the 71st season of the Isthmian League, which is an English football competition featuring semi-professional and amateur clubs from London, East and South East England.
League consisted of three divisions.
Division Two was divided into two sections.
Sutton United won the league for the second season in a row and finally were promoted to the Conference.
Division One consisted of 22 clubs, including 16 clubs from the previous season and six new clubs: Two clubs relegated from the Premier Division: Two clubs promoted from Division Two North: Two clubs promoted from Division Two South: