Bulgaria's parliament has approved the European Union accession treaty that will enable the country to become a member state.
Bulgarian leaders signed the treaty in Luxembourg last month
Bulgaria and neighbouring Romania signed the treaties last month, paving the way for them to join in 2007.
MPs in Sofia overwhelmingly backed the vote, which took place ahead of elections in June.
The treaties contain a safeguard clause delaying entry for a year if either country fails to meet EU standards.
The EU wants the independence of the judiciary to be strengthened and more efforts to tackle corruption in what will be its poorest member states.
If Bulgaria and Romania join in 2007, it will be the fifth enlargement of the EU project that would then have a total of 27 member states.
In May last year, eight of the 10 new member states were former communist countries.
Bulgaria and Romania missed that first round of EU expansion into eastern Europe because they had failed to implement sufficient democratic and market reforms.
A recent poll showed that 70% of Bulgarians are in favour of their country joining the EU in January 2007.