Polish President Lech Kaczynski said he was confident that Ukraine would join the European Union by 2020.
Kaczynski said the EU should continue expanding and that "by 2020 we (the EU) will have achieved the goal" of Ukrainian membership.
"There is no rationale to limit the EU to 27 members," he said.
Poland, which joined the EU in 2004, has close ties with Ukraine, and Kaczynski said Warsaw would help its neighbor in any way it could to join the European bloc and NATO.
He said the country of 47 million has tremendous resources and would help bring stability and democracy to the region.
Kaczynski acknowledged Ukraine faced political and economic problems, and said the country would require 10 years to reform its economy in order to qualify for EU membership. "But if it's 13 years, that's OK, too," he added.
His comments came amid Ukraine's worst political crisis since December 2004. The government of Prime Minister Viktor Yanukovich is openly defying President Viktor Yushchenko, who has dissolved Parliament and called for new elections.
The Polish president spoke during an informal meeting on the future of Europe with the presidents of Germany, Portugal, Italy, Finland, Hungary, Austria, Poland and Latvia. Austrian President Heinz Fischer said his country would host the meeting in 2008.
The leaders discussed the future of Europe, foreign policy and climate change, Latvian President Vaira Vike-Freiberga told reporters. In written statements after the meeting, they also stressed the need to adopt a constitution to improve the EU's decision-making processes, though Kaczynski said Poland was still not prepared to ratify the charter.
"We believe that changes are necessary," he said, "but Poland is ready to work on the text."
The Federation Council may gather for the meeting on October 4 to consider new laws on the accession of new territories to Russia after the referenda