The 1991 All Japan Sports Prototype Car Endurance Championship was the ninth season of the All Japan Sports Prototype Championship. The 1991 champion was the #23 Nissan Motorsports Nissan R91CP driven by Kazuyoshi Hoshino and Toshio Suzuki.
All races were held in Japan.
| Round | Race | Circuit | Date | |
|---|---|---|---|---|
| 1 | All Japan Fuji 500 km | Fuji Speedway | 10 March | |
| 2 | All Japan Fuji 1000 km | Fuji Speedway | 5 May | |
| 3 | All Japan Fuji 500 Miles | Fuji Speedway | 21 July | |
| 4 | International Suzuka 1000 km | Suzuka Circuit | 25 August | |
| 5 | SUGO Inter 500 km | Sportsland SUGO | 16 September | |
| 6 | Interchallenge Fuji 1000 km | Fuji Speedway | 6 October | |
| 7 | SUGO Inter 500 Miles | Sportsland SUGO | 3 November |
Season results as follows:[1]
| Round | Circuit | Winning Team |
|---|---|---|
| Winning Drivers | ||
| 1 | Mt. Fuji | |
 Kazuyoshi Hoshino Toshio Suzuki | ||
| 2 | Mt. Fuji Report | |
| Kazuyoshi Hoshino Toshio Suzuki | ||
| 3 | Mt. Fuji | |
| Hitoshi Ogawa Masanori Sekiya | ||
| 4 | Suzuka Circuit Report | |
| 5 | Sportsland SUGO Report | |
 Geoff Lees Eje Elgh | ||
| 6 | Mt. Fuji | |
| Kazuyoshi Hoshino Toshio Suzuki | ||
| 7 | Sportsland SUGO |
|
| Rank | width=160 | Drivers | width=240 | Number/Team | Points | Wins |
|---|---|---|---|---|---|---|
| 1 | Kazuyoshi Hoshino Toshio Suzuki |
| 87 | 3 | ||
| 2 | Hitoshi Ogawa Masanori Sekiya | 85 | 1 | |||
| 3 | Geoff Lees | 54 | 1 | |||
| 4 |  Volker Weidler Akihiko Nakaya |
| 52 | 0 | ||
| 5 |
| 52 | 0 |
