Ukrainian Prime Minister Yulia Tymoshenko's party has nominated her as its candidate for president.
Leaders of the bloc told a rally in Kiev's Independence Square Saturday that the decision was unanimous.
Ukrainian opposition leader Viktor Yanukovych launched his campaign for the presidency on Friday.
Mr. Yanukovych, who has promised to end the economic problems he says were caused by his pro-western rivals, is considered the front-runner for the January 17 election.
Recent opinion polls show Mr. Yanukovych leading with support from 24 to 28 percent of the voters, and Prime Minister Tymoshenko in second with about 15 percent.
Mr. Yanukovych was initially declared the winner of the last presidential poll in 2004, but the Supreme Court annulled his victory after mass protests and charges the vote was rigged.
Ms. Tymoshenko led the so-called Orange Revolution demonstrations alongside now President Viktor Yuchshenko, who won the re-run election in early 2005.
The embattled Mr. Yushchenko is currently in fourth place in election opinion polls, behind former parliament speaker Arseniy Yatsekniuk in third. Both have under 10 percent support.
The election comes as debate rages in Ukraine over the country's future ties to Russia, NATO and the European Union.
Tensions between President Yushchenko and Prime Minister Tymoshenko have all but paralyzed governance in Ukraine, which has also been hit hard by the global economic downturn.
Some information for this report was provided by AFP.