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.
<span style="font-size:85%">* Abbreviations: shd = short-head; nk = neck</span>
Further details of the winner, Mill Reef.