Between 35,000 and 40,000 people attended the protest, organisers said.
Thousands of protesters marched in Serbia's capital Belgrade on Saturday for the third week in a row against what they say is a crackdown by the government of President Aleksandar Vucic on opposition parties and the media.
Some chanted "Vucic, thief" at the latest rally in the first significant opposition demonstrations since spring 2017, when thousands of young Belgraders protested for weeks against Vucic's presidential victory.
"People are silent because of fear, because the spoken word has become dangerous, you can lose your head as I almost lost mine," said journalist Milan Jovanovic.
His Belgrade house was burnt down earlier this month in a molotov cocktail attack that his lawyer says was related to the journalist's work revealing corruption.
"But Serbia has woken from its hibernation and decided not to be silent," Jovanovic said before the start of Saturday's march.
Between 35,000 and 40,000 people attended the protest, organisers said. The police did not immediately offer a crowd size estimate, but have challenged the 20,000 number given by organisers for the previous Saturday's protest.
Vucic, a hardline nationalist-turned-European, is accused by the opposition and civil society of having established autocratic rule and full control over media, using them to campaign against opponents.
"They can march as much they want, without violence," Vucic said on Saturday.
"But the people understand very well that after each demonstration me and my party are stronger."
The protests were first called by opposition parties after one of their leaders was beaten ahead of a political gathering in central Serbia last month.
The opposition Alliance for Serbia (SZS), an umbrella of parties from across the political spectrum, accused the attackers of being supporters of Vucic's ruling Serbian Progressive Party (SNS), a claim the authorities denied.
In its latest report on Serbia, the European Parliament "strongly" encouraged Serbian authorities" to "improve the situation regarding freedom of expression and freedom of the media".