Protesters say the government is pushing through laws that will harm the country's fight against corruption.
When it comes to fighting corruption, some are prepared to walk the extra mile.
One man marched 450 kilometres across Romania — attracting many supporters along the way — to attend an anti-graft demonstration in Bucharest.
Protesters are upset at government moves they say would put the justice system partially under political control and decriminalise some corruption offences.
"This is why people are in the streets, because from month-to-month we saw that politicians are still trying to demolish the rule of law in Romania," Attila Biro, a journalist at RISE Project, told Euronews.
Some 50,000 people joined the demonstration in Romania's capital, braving the elements, as thousands more demonstrated in cities across the ex-communist state.
"We want a free country, we want freedom and free justice in our country. It's all about the future of our children," said Halina, a protester at Saturday evening's march.
Romania, which joined the EU just over a decade ago, is ranked one of the bloc's most corrupt states by Transparency International.