The 1989–90 Southern Football League season was the 87th in the history of the league, an English football competition.
Dover Athletic won the Premier Division but were not promoted due to ground grading issues and a place in the Football Conference was taken by runners-up Bath City. Four bottom clubs were relegated to the Southern and Midland divisions, while champions and runners-up of lower divisions get a places in the next Premier Division season. Banbury United, Hounslow, Sandwell Borough and Sheppey United left the league.
The Premier Division consisted of 22 clubs, including 17 clubs from the previous season and five new clubs:
| Competition: | Southern Football League Premier Division |
| Season: | 1989–90 |
| Winners: | Dover Athletic |
| Promoted: | Bath City |
| Relegated: | Alvechurch Ashford Town (Kent) Corby Town Gosport Borough |
| Matches: | 462 |
| Total Goals: | 1302 |
| Prevseason: | 1988–89 |
| Nextseason: | 1990–91 |
The Midland Division consisted of 22 clubs, including 17 clubs from the previous season and five new clubs:
Also, at the end of the previous season Forest Green Rovers was renamed Stroud and Ashfield Hightree was renamed Sandwell Borough.
| Competition: | Southern Football League Midland Division |
| Season: | 1989–90 |
| Winners: | Halesowen Town |
| Promoted: | Halesowen Town Rushden Town |
| Relegated: | Banbury United Sandwell Borough |
| Matches: | 462 |
| Total Goals: | 1393 |
| Prevseason: | 1988–89 |
| Nextseason: | 1990–91 |
The Southern Division consisted of 22 clubs, including 18 clubs from the previous season and four new clubs:
Also, at the end of the previous season Thanet United reverted name to Margate.
| Competition: | Southern Football League Southern Division |
| Season: | 1989–90 |
| Winners: | Bashley |
| Promoted: | Bashley Poole Town |
| Relegated: | Sheppey United |
| Matches: | 462 |
| Total Goals: | 1315 |
| Prevseason: | 1988–89 |
| Nextseason: | 1990–91 |