The 1990–91 South Midlands League season was 62nd in the history of South Midlands League.[1] [2] [3] [4] [5]
| Competition: | South Midlands League Premier Division |
| Season: | 1990–91 |
| Winners: | Thame United |
| Promoted: | Thame United |
| Relegated: | None |
| Prevseason: | 1989–90 |
| Nextseason: | 1991–92 |
The Premier Division featured 17 clubs which competed in the division last season, along with 3 new clubs:
Also Milton Keynes/Wolverton Town changed their name to Wolverton.
| Competition: | South Midlands League Division One |
| Season: | 1990–91 |
| Winners: | Buckingham Athletic |
| Promoted: | Buckingham Athletic Oxford City |
| Relegated: | None |
| Prevseason: | 1989–90 |
| Nextseason: | 1991–92 |
The Division One featured 14 clubs which competed in the division last season, along with 4 new clubs: