Polish Prime Minister Leszek Miller is quitting as head of his Democratic Left Alliance, a spokesman has announced.
Miller became prime minister in October 2001
Mr Miller will stay on as PM despite slumping popularity for his party.
Its support has dropped sharply as budget cuts have been introduced ahead of the country's EU membership in May, aimed at bringing its economy into line with EU requirements.
His decision will take effect at a party convention on 6 March, said spokesman Jerzy Wenderlich.
The party remained "fully behind" the cuts, Mr Wenderlich added.
Recent opinion polls suggest the party's support has fallen to as little as 12%.