The 2001 No Mercy was the fourth No Mercy professional wrestling pay-per-view (PPV) event produced by the World Wrestling Federation (WWF, now WWE). The event took place on October 21, 2001, at the Savvis Center in St. Louis, Missouri. It was the final No Mercy event held under the WWF name as the promotion was renamed to World Wrestling Entertainment (WWE) in May 2002. It was also the final No Mercy held before the introduction of the brand extension in March 2002.

The main event was a Triple Threat No Disqualification match—a match involving three competitors against each other and it would be decided only through pinfall or submission. The match was contested for the WWF Championship. Stone Cold Steve Austin defended the title against Kurt Angle and Rob Van Dam. Austin pinned Van Dam after a Stone Cold Stunner to retain the title.

The undercard featured The Rock versus Chris Jericho for the WCW Championship, The Undertaker versus Booker T, Dudley Boyz (Bubba Ray Dudley and D-Von Dudley) versus Big Show and Tajiri for the WWF Tag Team Championship, Christian versus Edge in a Ladder match for the WWF Intercontinental Championship, Torrie Wilson versus Stacy Keibler in a Lingerie match, Test versus Kane and Hardy Boyz (Matt Hardy and Jeff Hardy) versus Lance Storm and The Hurricane for the WCW Tag Team Championship.