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 | #23 Nissan Motorsports Nissan R91CP |
 Kazuyoshi Hoshino Toshio Suzuki | ||
| 2 | Mt. Fuji Report | #23 Nissan Motorsports Nissan R91CP |
| Kazuyoshi Hoshino Toshio Suzuki | ||
| 3 | Mt. Fuji | #36 Toyota Team TOM'S Toyota 91C-V |
| Hitoshi Ogawa Masanori Sekiya | ||
| 4 | Suzuka Circuit Report | #38 Toyota Team SARD Toyota 91C-V |
 Roland Ratzenberger  Pierre-Henri Raphanel Naoki Nagasaka | ||
| 5 | Sportsland SUGO Report | #37 Toyota Team TOM'S Toyota 91C-V |
 Geoff Lees  Eje Elgh | ||
| 6 | Mt. Fuji | #23 Nissan Motorsports Nissan R91CP |
| Kazuyoshi Hoshino Toshio Suzuki | ||
| 7 | Sportsland SUGO | #17 TWR Suntech Jaguar XJR-14 |
 David Brabham  Teo Fabi | ||
| Rank | Drivers | Number/Team | Points | Wins |
|---|---|---|---|---|
| 1 | Kazuyoshi Hoshino Toshio Suzuki | #23 Nissan Motorsports Nissan R91CP | 87 | 3 |
| 2 | Hitoshi Ogawa Masanori Sekiya | #36 Toyota Team TOM'S Toyota 91C-V | 85 | 1 |
| 3 | Geoff Lees | #37 Toyota Team TOM'S Toyota 91C-V | 54 | 1 |
| 4 |  Volker Weidler Akihiko Nakaya | #27 From A Racing Nissan R90CK | 52 | 0 |
| 5 |  George Fouché Steven Andskär | #100 Trust Racing Porsche 962C | 52 | 0 |
