In a statement, Leonid Kravchuk, Leonid Kuchma and Viktor Yushchenko expressed "solidarity" with peaceful rallies.
Thousands of protesters remain camped in Kiev's Independence Square, and are continuing to block the main government's building.
They are angry at the government's last-minute decision not to sign an association deal with the EU.
German Foreign Minister Guido Westerwelle on Wednesday visited protesters on Independence Square, saying that "the gates of the European Union are still open".
Meanwhile, Russia - which wants Kiev to join the Moscow-led Customs Union - has urged the West not to interfere in Ukraine.
"We express solidarity with the peaceful civic actions of hundreds of thousands of young Ukrainians," the three former presidents said in a statement.
They condemned "the excessive use of force against peaceful demonstrators" and called on all sides to refrain from further violence.
They urged protest leaders and the government to engage in "open dialogue", taking into account "the European aspirations of the Ukrainian people".
Ukraine's special police, Berkut, has been widely condemned for beating protesters on Independence Square last Saturday.
A number of people were injured as the police cleared the protest camp - known as Maidan.
The opposition - which has since retaken the square - is demanding the resignation and punishment of the interior minister.
On Sunday, clashes erupted again at the presidential administration building in central Kiev.
Dozens of protesters - along with a number of journalists - were injured.
Some of them are reported to be in intensive care.
Nine people have been detained for two months while they await trial, but two protesters have since been freed, Ukrainian MP Roman Ilyk was quoted as saying by the Ukrainska Pravda news website.
Friends of those held say they were ordinary citizens rather than activists or protest organizers.
Protest rallies have continued across Ukraine, including a big demonstration in the western city of Lviv.
Pro-presidential supporters have also staged a counter-rally in the eastern city of Donetsk, Ukraine's industrial powerhouse which has close ties to Russia.
Meanwhile, Russian Foreign Minister Sergei Lavrov said the West should not interfere in the Ukrainian crisis.
"I hope that Ukrainian politicians will be able to resolve the situation peacefully," he said at a meeting with NATO foreign ministers in Brussels on Wednesday.
NATO had earlier condemned the use of "excessive force" against pro-European protesters.
Pressure from Russia Mr Lavrov's comments came after Ukraine's Prime Minister Mykola Azarov called on the opposition to stop escalating political tensions.
He warned protesters that anybody found guilty of violating the constitution and laws would be punished.
Mr Azarov was speaking in a live broadcast from the first cabinet meeting since mass street protests began just over a week ago.
The protests are the largest since the pro-democracy Orange Revolution in 2004.
They were sparked after President Viktor Yanukovych abruptly froze plans to sign the EU trade and reform deal last month, under pressure from Russia.
Mr Yanukovych is continuing his official visit to China in what is reported to be a bid to forge closer economic ties.
Another Ukrainian delegation is holding talks with Russian Prime Minister Dmitry Medvedev in Moscow.
Mr Azarov said earlier this week he would be sending representatives to Brussels to renew talks on the EU deal.
Both he and Mr Yanukovych are facing calls from the protesters for their resignations.
The three former presidents said demonstrators felt a "deepening distrust" towards the government.
Mr Kravchuk, 79, became Ukraine's first president after it gained independence from the USSR in 1991.
He was succeeded by Mr Kuchma, now 75, in 1994.
Mr Yushchenko came to power in 2005.
Ukraine's post-USSR presidents
- Leonid Kravchuk (1991-1994)
- Leonid Kuchma (1994-2005)
- Viktor Yushchenko (2005-2010)
- Viktor Yanukovych (2010-present)
Source: BBC News