Romanian President Traian Basescuon Wednesday signed a decree promulgating the law under which Romania ratified the Lisbon Treaty.
The Romanian Parliament ratified the treaty in the February 4 sitting, with 387 favorable votes in favor, one against and one abstention.
Romania is the fourth EU state to ratify the Lisbon Treaty, after Hungary, Slovenia and Malta.
The EU treaty was designed to replace the constitution scuppered by Dutch and French referendums in 2005 and to end years of diplomatic wrangling over reform of the bloc's institutions.
All 27 member states need to ratify the treaty, meaning that even a small member country could topple the treaty.
According to the schedule, the treaty signed in Lisbon must be ratified individually by all member states before it comes into effect, as planned, on January 1, 2009.
Like the rejected constitution, the treaty proposes a new presidential post and a European foreign policy supremo.
It also includes a European charter of fundamental human and legal rights, which Britain and Poland have refused to make binding.