Caroline Jackson, one of the South West's Conservative Euro MPs, says she will be standing down at the next European elections in two years' time.
Dr Jackson is the only woman out of 27 British Tory MEPs
In 2004 she was number two on the Conservative list in the South West and is currently the only woman out of 27 Tory MEPs from Britain.
Penzance-born Dr Jackson, who is 60, has been an MEP since 1984.
She says she hopes her announcement will allow time for another woman candidate to be found to succeed her.
Dr Jackson said: "I'm not a militant feminist but I do think that we need to have a delegation in Strasbourg and Brussels that better reflects the make-up of our society.
"Currently I am the only woman out of 27 Conservative MEPs.
"If I'm not there they can't have a group photo taken because it looks like something from the 1930s, when most politicians were men."
Dr Jackson said she has enjoy her time in the European Parliament and will "certainly miss it" when she leaves in 2009.
The South West MEPs cover Devon, Cornwall, Somerset, Dorset, Bristol, Gloucestershire and Wiltshire.