Winx (foaled 14 September 2011) is a retired champion Australian Thoroughbred racehorse and active broodmare. She won 37 of 43 career starts, including, between May 2015 and her retirement in April 2019, her last 33 races in succession, including 25 Group 1s (a world record), at distances ranging from 1300 metres (roughly 6+1⁄2 furlongs) to 2200 metres (roughly 11 furlongs). In the World's Best Racehorse Rankings, she was the second-ranked filly or mare in 2015, improving in 2016 to become both the world's top-ranked filly or mare and the world's top-ranked turf horse. She retained this ranking in 2017 and in 2018 was co-ranked as the best horse in the world. In 2017 she was inducted into the Australian Racing Hall of Fame, only the third horse to earn this honour while still in training. Over her career, she earned more than 26 million Australian dollars.

Winx began her racing career with three straight wins but then won only one race in her next seven starts. Towards the end of her three-year-old campaign, she rebounded to win two races in May 2015, including the Group 1 Queensland Oaks, to start her winning streak. As a four-year-old, she was named the 2015/6 Australian Horse of the Year and middle distance champion after a seven race campaign that included wins in the W. S. Cox Plate and Doncaster Mile. In the 2016/7 season, she successfully defended her 2015 Cox Plate win with a commanding eight length victory over rival Hartnell. She completed the season with a win in the Queen Elizabeth Stakes and was again named Horse of the Year.

For the 2017/18 season, she earned her third Horse of the Year honour after recording seven straight wins, including her third victories in the Cox Plate, Chipping Norton and George Ryder and her second win in the Queen Elizabeth. In the 2018/19 season, Winx began her seven-year-old campaign on 18 August in a race renamed in her honour and in doing so extended her winning streak to an Australasian record of 26, since extended to 33. Winx became the first horse in history to win the prestigious Cox Plate four times. She won the 2018 Secretariat Vox Populi Award, the top choice among race fans in a record 60 countries.

She finished her career on 13 April 2019 at Randwick racecourse by winning the Queen Elizabeth Stakes for the third time. She was then retired to be a broodmare.

Winx is a bay mare bred in Australia by John Camilleri's Fairway Thoroughbreds. She was foaled on 14 September 2011 at Coolmore Stud, Jerrys Plains in the Hunter Valley of New South Wales. She was sired by the Irish-bred Street Cry, who won the Dubai World Cup in 2002 before becoming a very successful breeding stallion in North America and Australasia. His other progeny included Zenyatta, Street Sense, Shocking and Whobegotyou. Winx's dam, Vegas Showgirl, was a stakes winner in New Zealand who was bought by Fairway Thoroughbreds in 2008 as a broodmare prospect for A$455,000.

Winx stood and nursed soon after foaling and quickly stood out as "a leggy Elle Macpherson type". She was sold as a yearling for $230,000 at the 2013 Magic Millions Gold Coast sale. She was part of a draft of horses from Coolmore Stud and was selected by Mulcaster Bloodstock (Guy Mulcaster) to be purchased "to a budget" by a partnership of Magic Bloodstock Racing (owned by Peter Tighe and his wife Patty), Richard Treweeke and Debbie Kepitis (daughter of famed owner Bob Ingham). The name "Winx" was inspired by her dam's name "Vegas Showgirl", and a memory of Treweeke that in Las Vegas burlesque shows from the 1970s and 1980s, "men in the front row would wink at the exotic dancers". Winx raced in Magic Bloodstock's silks: dark blue with white epaulettes and a large white "M", and was trained by Chris Waller.

Unlike many elite racehorses, Winx does not have a particularly long stride – her stride was measured at 6.76 metres (22.2 ft) compared to nearly 8.5 metres (28 ft) for Black Caviar and Phar Lap. Rather, her success has been attributed to a "freakish" cadence that allows her to take 14 strides every 5 seconds, compared to 12 for her rivals. "This means she can settle or accelerate at any time during a race", said Dr. Graeme Putt, who has studied the science of racehorse success. "I think this makes her unique."

After two racecourse trials, Winx made her competitive debut on 4 June 2014 in a maiden race and won over 1100 metres at Warwick Farm Racecourse. Later that month, on her second and final race of the season, she won over 1400 metres at Rosehill Racecourse in Sydney.