Denmark will hold an early general election on 8 February, the ruling Liberal Party said on Tuesday.
Mr Rasmussen is widely expected to win again
The party, led by Prime Minister Anders Fogh Rasmussen, has been in power since November 2001. It governs in a coalition with the Conservative Party.
Under the constitution, the prime minister can set an election date at any time during the government's four-year term.
Opinion polls indicate that the ruling coalition will win.
The centre-right government has tightened Denmark's immigration laws and supported the US-led war that toppled Iraqi President Saddam Hussein.
Denmark has 525 troops in Iraq, and correspondents say a change of government would be unlikely to lead to their early withdrawal.
Like the UK, Denmark has stayed out of the eurozone.