German Chancellor Angela Merkel has urged EU leaders to be ready to compromise on a new constitutional treaty before a crucial summit.
Mr Kaczynski and Mrs Merkel held crucial talks in Germany
Mrs Merkel met Polish President Lech Kaczynski in Germany for crucial talks on the simplified treaty.
Germany, the current holder of the EU presidency, wants states to agree to a road map for a new constitution at next week's summit in Brussels.
Mr Kaczynski has threatened to veto any deal reducing Poland's voting rights.
'Time to act'
Speaking on her weekly video podcast, released just before she met with Mr Kaczynksi on Saturday, Mrs Merkel said Europe needed to "recover its ability to act".
"For [the timetable] to be agreed on, readiness to compromise on the part of everyone will be necessary," she said.
"We are working on it and thank many member states for pursuing the same goal."
She urged leaders from the EU's 27 member states to act quickly to resolve the constitutional crisis.
"We need a new contractual basis for this, but we also must not devote our attention to ourselves for too long," she said.
French and Dutch voters rejected a proposed EU constitution in 2005.
The new, simplified treaty is expected to address demands for institutional change to help the EU to operate more efficiently.
But Mr Kaczynski has threatened to block efforts to draft it next week because of the proposed changes to the bloc's national voting system.
The BBC's Adam Easton in Warsaw says Poland currently has an extraordinarily good deal compared to its size.
However, under the "double majority" system written into the constitution three years ago, it stands to be one of the biggest losers, our correspondent says.
Poland says accepting the system would be a capitulation, because it would give its neighbour, Germany, far more weight than it has now and Poland far less.
Mr Kaczynski has therefore said he wants European leaders to discuss what he believes is a fairer alternative - calculating voting rights according to the square root of each country's population, rather than simply according to population.
If Poland is not allowed to have its say, it will use its veto, Mr Kaczynski has warned.
The president and his twin brother, Prime Minister Jaroslaw Kaczynski, say their plan "is worth dying for".
Our correspondent says the chances for an agreement next week are not looking good.
Berlin has identified seven outstanding problems to be discussed at the summit and the voting system is not among them.
Mrs Merkel has admitted it will take a "Herculean" effort to win Poland round.