The 1997 Winchester by-election was a by-election to the UK House of Commons in the constituency of Winchester, Hampshire. Winchester was initially declared to have been won by Mark Oaten (Liberal Democrat) with a majority of two votes at the general election on 1 May 1997, but following a legal challenge, a new election was allowed by the High Court. The by-election, held on 20 November, was won by Oaten with a majority of 21,556.