The horse - a piece of contemporary art by "shock" Italian artist Maurizio Cattelan - was bought for £619,750 at Christie's in London.
Entitled La Ballata di Trotsky, the horse fetched a record price for a Cattelan work and much more than the estimated £400,000.
The taxidermied racehorse called Tiramisu - after the Italian dessert - was shown two years ago at the Tate's controversial Abracadabra show, also featuring Cattelan's suicide squirrel.
Christie's said the unorthodox Cattelan creation, completed in 1996, was typical of his "clever" and "sarcastic" works.
"By making ironic references to other artists, especially to his Italian predecessors, he re-writes art history from a charlatan's point of view," said the sale's description of Cattelan's work.
"His work is subversive, humorous and sharply ironic, frequently mocking the art market by attacking the very infrastructure and presentation that supports it."
'Playful'
Last month, Cattelan, 40, sold another of his controversial pieces called The Ninth Hour, showing the Pope being crushed by a meteorite, for £619,500 in New York.
Cattelan's horse hangs in a leather harness exactly like the ones used to transport racehorses without injury.
But the animal has also had its legs lengthened since becoming an art exhibit.
The horse's body was given to the artist by a veterinary college after it died from natural causes.
When it was shown at the Tate's Abracadabra show, the horse was given the name Twentieth Century.
The Abracadabra was billed as capturing a "playful" mood in contemporary art and featured 15 artists.
Cattelan's squirrel piece was called Bidibidobidiboo. The animal, again stuffed, was slumped on a kitchen this time apparently having shot itself.
But Cattelan has also created more sober works, including one called Stadium, a seven-metre table football machine for 11-a-side play.
The horse was sold as part of Christie's Contemporary Art Sale, which will continue on Friday.
Other artists to be featured are the equally controversial British duo Gilbert and George and Tracey Emin.