"We now have 27 member states. I am deeply convinced this is not the end... The EU, a successful experiment without precedent in human history, cannot be closed to those who wish to join ... not only in the Balkans but also countries like Georgia."
The Lisbon Treaty is designed to give the 27-nation bloc a long-term president and a stronger foreign policy chief.
It can only take effect when all member states have approved it.
Vaclav Klaus, the Czech president, set out his terms on Friday for signing the treaty, demanding an exemption to protect the Czech Republic from post-war property claims and safeguard the sovereignty of the judiciary.
Poland and Britain have already won opt-outs on the application of some of the provisions of a Charter of Fundamental Rights which will be given binding force when the Lisbon Treaty is ratified.
Last week, Irish voters backed the treaty with a large majority in a referendum.
The EU hopes the treaty, which also aims to streamline EU decision-making via increased majority voting in the 27-nation bloc, will be implemented in 2010.