Speaking before tens of thousands of supporters at a rally in the capital Kiev, he predicted Sunday’s vote “will not be an easy political walk”.
Mr Yushchenko said “there are some forces preparing to disrupt and they are preparing brigades, groups who are preparing to come to Kiev.”
Flanked by family and well-known supporters including Ukraine’s world heavyweight boxing champ Vitali Klitschko, Mr Yushchenko also praised the crowd for changing the country without bloodshed.
He said they “peacefully, beautifully, elegantly and without any drops of blood” changed Ukraine.
Mr Yushchenko vowed to work to unite his country badly split over an earlier election ruled fraudulent and thrown out by the country/s Supreme Court.
“I will be the president of all Ukraine. I will do everything for the unity of Ukraine,” he said and repeated earlier pledges to pull Ukrainian troops out of Iraq if elected.
He also called on his supporters to return to the square on the day of the vote and remain there “until we celebrate our victory”.
The mass rally marked exactly one month since the start of mass street protests against the official results of the earlier vote.
Sunday’s rerun election has assumed a major geopolitical significance as the country sits on the East-West fault line between former Soviet republics still dominated by Russia and long-established European and US democracies.
His pro-Moscow opponent, Prime Minister Viktor Yanukovich, was officially declared the winner in the earlier vote despite widespread claims of electoral fraud.
With Moscow worried that under his leadership, the nation of 48 million people will focus on building stronger bonds with Western Europe., Mr Yushchenko has also been busy allaying the Kremlin’s nerves.
If he wins Sunday’s poll, he says Ukraine will maintain its deep historical and cultural bonds with Russia and pledged to make his first official visit to Russia.
He’s also promised to examine making Russian a second official language and to introduce dual Ukrainian-Russian citizenship.
The approach seems to be working, with President Vladimir Putin backing away from his previous criticism of the 50-year-old opposition leader.
President Putin dismissed suggestions an opposition victory would deal him a personal defeat, saying he could work with either candidate.
The European Union has taken a close interest in the election.
Dutch Foreign Minister Ben Bot, whose country holds the rotating EU presidency, says he expects Mr Yushchenko to appoint a prime minister from the other camp if he wins.
Stressing that the EU has no official position on the matter, he believed the appointment of a prime minister from the opposite camp would be a way of keeping the country together.
But Mr Yushchenko has ruled out naming Mr Yanukovich to any cabinet position.
“We aren’t considering under any circumstances the possibility of Yanukovich’s participation, such as Yushchenko president and Yanukovich as prime minister or any other position in my government,” he told the Interfax news agency.