The Czech Constitutional Court has ruled that the European Union's reform treaty conforms with Czech law, allowing parliament to proceed with ratification. Ireland is now the only member state which has rejected the treaty.
The lack of Czech ratification so far has raised doubts in the EU about the likely performance of the 6-month Czech EU presidency, starting in January.
The court's finding that the treaty does not infringe the Czech constitution is a big step forward in the ratification process, but does not guarantee smooth approval in both houses of parliament.
The treaty faces opposition from some government backbenchers, cheered on by the eurosceptic president Vaclav Klaus, who rejects any transfer of national powers to the EU.
Prime Minister Mirek Topolanek, who also dislikes the treaty but grudgingly backs it as a price worth paying for EU membership, has said ratification is unlikely to be completed before the year's end.
Mr Topolanek has said some of his party's deputies may refuse to support Lisbon unless the leftist opposition backs plans to build a US anti-missile defence radar southeast of Prague.