More than 1,000 Polish nationalists and followers of right-wing Catholic groups gathered in the capital Warsaw on midday Saturday to protest perceived EU interference in national politics.
Counter rallies by backers of the 28-member bloc were planned for later in the afternoon. The europhiles' motto was "We are and will remain in Europe."
Warsaw-based medical student Kondrian, 24, wants Poland to regain its full sovereignty. "It would be best if we left the EU," he told dpa ahead of a mass in St Florian's Cathedral, where anti-EU protesters were gathering.
"We are not against Europe, but we don't want anyone telling us what to do," said 50-year-old engineer Piotr Goszczynski, adding this was true both for the acceptance of refugees as well as interior politics.
The policies of the ruling national-conservative Law and Justice party (PiS) have been causing friction with Brussels for months.
The EU has launched an investigation into new laws on the country's public broadcasters, constitution and police powers, which are seen to undermine the bloc's fundamental values.