Big Brother 2005, also known as Big Brother 6, was the sixth series of the British reality television series Big Brother, in which a number of contestants live in an isolated house trying to avoid being evicted by the public with the aim of winning a large cash prize at the end of the run.

The series launched on Channel 4 on 27 May 2005 and ended on 12 August 2005, lasting eleven weeks, at the time the longest the programme had lasted, Davina McCall returned as host for her sixth consecutive year. Thirteen housemates entered on launch night with an additional three being introduced in Week 4, this was the first series where late entry housemates survived public votes and made it to the final. Anthony Hutton was chosen as the winner on Day 78, receiving £50,000, Eugene Sully who finished second received the other half of the prize money due to a task on Day 76.

Makosi and Craig returned in 2009 to compete in a task for a few hours, in 2010 Makosi was a contestant in Ultimate Big Brother. She entered on Day 1 and became the second Ultimate housemate to be evicted on Day 11. Anthony also returned as a guest to have a picnic date with Makosi. The Big Brother eye for this series was also used for the Serbian Big Brother series, Veliki brat.