Mark Oaten (born 8 March 1964) is a British politician who was a senior member of the Liberal Democrats. He served as the Member of Parliament (MP) for Winchester from 1997 to 2010.

Born in Watford, Hertfordshire, Oaten became a councillor in local government, joining the centre-left Social Democratic Party, which merged with the Liberal Party to form the Liberal Democrats in 1988. He became the party's Home Affairs spokesman in 2003. He stood for the position of Leader of the Liberal Democrats in 2006, but withdrew from the contest he was later hit by a series of scandals which also led to his resignation as Home Affairs spokesman. He did not seek re-election to the House of Commons at the 2010 general election.

Following his retirement from active politics, Oaten published two books, before becoming executive of the International Fur Trade Federation in 2011.