Protest organisers demanded the government resign over recent legislation and measures that they say are tailor-made to advance the interests of corrupt politicians.
Protesters also called for the perpetrators of the previous night's violence to be prosecuted.
The demonstrations on Saturday proceeded peacefully, with approximately 25,000 people taking part in the capital Bucharest, according to the Agerpres news agency.
Some 10,000 others gathered in Iasi, approximately 8,000 people in Timisoara and 5,000 more in Sibiu, the agency reported. Smaller protests were also held in other cities across the country.
According to the Mediafax news agency, 452 people, including 35 police, were injured when Friday night's protest turned violent.
A small group had attempted to storm government offices and clashed with riot police.
President Klaus Iohannis, an opponent of the Socialist Democrat-led government and a vocal critic of its corruption policy, criticized the police reaction as "brutal."
The ruling coalition has passed laws limiting the power of the anti-corruption agency DNA and sacked its head, Laura Kovesi.
Romania, a former Communist bloc country, joined the European Union in 2008, but remains under a special mechanism monitoring the status of its judicial reforms and the fight against corruption.