Thousands of people hold up Czech National flags during an anti-governmental demonstration in Prague on September 16, 2023. AFP
The small, non-parliamentary PRO party organising the protest estimated attendance at 101,662 people on its website, while the Czech news agency CTK put the number at around 10,000.
Waving Czech flags and urging the government of right-wing Prime Minister Petr Fiala to resign, protesters also bemoaned the EU member's economic slowdown.
The Czech economy has been stagnant for a year, while inflation is only slowly retreating from record-high annual levels that peaked at 18 percent in September 2022.
"I'm here for the children, because that's our future, and I'm afraid of the future," protester Hana Smolikova told AFP at the rally in Prague's central Wenceslas Square, worried by the high prices "of everything".
Protester Pavel Husek said the government "should stop supporting only Ukraine and start paying attention to their citizens".
Fiala's five-party coalition government has provided Ukraine with substantial humanitarian and military aid since the Russian invasion started in February 2022.
Prague police said they had detained a man wearing the logo of the infamous Wagner group of Russian mercenaries at the rally, called "Czechia Against Government".