Leonid Kravchuk, Leonid Kuchma, and Viktor Yushchenko made a joint announcement throwing their support behind the protesters.
The protesters are demanding that President Viktor Yanukovych resign.
He angered the public when backed out of signing a trade agreement with the European Union, and instead announced that he would seek closer ties with Russia.
Many Ukrainians worry that Yanukovych is taking their country back under Russian influence and fear a loss of their independence from their former Soviet masters.
