Ukraine's lawmakers are set to ratify a landmark EU association agreement - in proceedings simultaneous with a session of the European Parliament.
Both sides will start the procedure at 10:00 GMT, in what Ukraine's president said would be a "historic" day.
But the implementation of a free trade deal - part of the package - has been postponed until 2016, apparently under pressure from Russia.
This comes as a fragile ceasefire largely holds in eastern Ukraine. There were reports of shelling around the government-held airport of Donetsk and other towns.
Pro-Russian rebels have been engaged in heavy fighting with government forces in the Donetsk and Luhansk regions since April - a month after Russia annexed southern Crimea peninsula.
Some 3,000 people have been killed over the past five months of conflict.
Russia denies sending troops and heavy weaponry to help the rebels, as alleged by Ukraine and the West.