| Location: | Longchamp Racecourse |
| Winning Horse: | Mill Reef |
| Next: | 1972 |
The 1971 Prix de l'Arc de Triomphe was a horse race held at Longchamp on Sunday 3 October 1971. It was the 50th running of the Prix de l'Arc de Triomphe.
The winner was Mill Reef, a three-year-old colt trained in England by Ian Balding and ridden by Geoff Lewis. Mill Reef won by three and one-and-a-half lengths from the two fillies Pistol Packer and Cambrizzia in a new race-record time of 2:28.3.
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| Pos. | Marg. | Horse | Age | Jockey | Trainer (Country) |
|---|---|---|---|---|---|
| 1 | Mill Reef (USA) | 3 | Geoff Lewis | Ian Balding (GB) | |
| 2 | 3 | Pistol Packer (USA) | 3 | Freddy Head | Alec Head (FR) |
| 3 | 1½ | Cambrizzia (FR) | 3 | Sandy Barclay | D. Watson (FR) |
| 4 | nk | Caro (IRE) | 4 | Jimmy Lindley | Albert Klimscha (FR) |
| 5 | ½ | Hallez (FR) | 4 | Lester Piggott | William Head (FR) |
| 6 | ½ | Royalty (GB) | 3 | Joe Mercer | Dick Hern (GB) |
| 7 | Bourbon (FR) | 3 | Yves Saint-Martin | Alec Head (FR) | |
| 8 | Arlequino (FR) | 3 | J. Massard | Geoffroy Watson (FR) | |
| 9 | One for All (USA) | 5 | Willie Carson | Horatio Luro (USA) | |
| 0 | Mister Sic Top (FR) | 4 | Jean-Claude Desaint | Gilbert Pezeril (FR) | |
| 0 | Miss Dan (FR) | 4 | J. Taillard | Philippe Lallie (FR) | |
| 0 | Armos (IRE) | 4 | G. Thiboeuf | Daniel Lescalle | |
| 0 | Ossian (FR) | 4 | L. Heurteur | Dick Hern (GB) | |
| 0 | Ramsin (FR) | 4 | Henri Samani | Geoffroy Watson (FR) | |
| 0 | Ortis (ITY) | 4 | Duncan Keith | Peter Walwyn (GB) | |
| 0 | Sharapour (FR) | 3 | William Williamson (AUS) | Francois Mathet (FR) | |
| 0 | Irish Ball (FR) | 3 | William Pyers (AUS) | Philippe Lallie (FR) | |
| 0 | Oarsman (GB) | 3 | Maurice Philipperon | John Cunnington | |
Further details of the winner, Mill Reef.[1]