| Competition: | Cypriot Third Division |
| Season: | 1990–91 |
| Winners: | Othellos Athienou FC (1st title) |
| Prevseason: | 1989–90 |
| Nextseason: | 1991–92 |
The 1990–91 Cypriot Third Division was the 20th season of the Cypriot third-level football league. Othellos Athienou FC won their 1st title.
Fourteen teams participated in the 1990–91 Cypriot Third Division. All teams played against each other twice, once at their home and once away. The team with the most points at the end of the season crowned champions. The first two teams were promoted to 1991–92 Cypriot Second Division. The last three teams were relegated to the 1991–92 Cypriot Fourth Division.
The 3rd-placed team faced the 12th-placed team of the 1991–92 Cypriot Second Division, in a two-legged relegation play-off for one spot in the 1991–92 Cypriot Second Division.
Teams received two points for a win, one point for a draw and zero points for a loss.