Prime Defender (30 March 2004 – 24 July 2012) was a British Thoroughbred racehorse.

Prime Defender was a chestnut horse with a white blaze bred by Christopher J Mason. He was one of the best horses sired by Bertolini a "high class sprinter" who won the July Stakes in 1998.^[2] He was trained by Barry Hills in Lambourn and owned by friends Steve Falle, Matt Franklin and James Sumsion.

As a three-year-old, Prime Defender won the European Free Handicap at Newmarket Racecourse in April and the Sandy Lane Stakes at Haydock Park in May. After a long break without a major win he won the Cammidge Trophy at Doncaster in March 2009. He recorded his most important victory as a six-year-old in August 2010 when he won the Group Two (Duke of York Stakes).^[3] Prime Defender holds the juvenile and overall track record at Wolverhampton.

Prime Defender was retired to Hedgeholme Stud in County Durham at the end of the 2011,^[4] but after having fertility problems he was returned to training the following year with the Nottinghamshire trainer Michael Appleby. He was being prepared for a return to racing when he died of a heart attack in a training gallop on 24 July 2012.^[5]