People are angry with President Vučić's government and his close ties with the tabloid media they claim incites hatred and promotes violence.
Thousands of people gathered on Saturday in the centre of Belgrade for the 'Serbia against violence' march.
It was the eighth week of protests in a row in the country's capital and this time extended to 20 other cities.
These included Serbia's next largest cities of Novi Sad and Kragujevac, and in the smaller towns of Kraljevo, Subotica, Vranje, Sabac and Leskovac.
The demonstrators, including members of some opposition parties are calling for the resignation of President Aleksandar Vučić, and also top representatives in media, the police force, and security services.
Critics of the president accuse him of authoritarianism and say the tabloid media his government is close to incites hatred and promotes violence. Protestors also want an end to reality TV shows.
What happened in May?
A growing number of cities are joining the demonstrations, triggered by a wave of outrage following two shootings in early May that left 19 people dead.
On 3 May, a 13-year-old student at a Belgrade school shot dead nine classmates and a security guard. Less than 48 hours later, a 21-year-old killed nine people in a central Serbian town.
Protesters are calling for government accountability and the resignation of the Minister of the Interior and the director of the Information and Security Agency.
The opposition has rejected an offer of dialogue from Vučić as well as early elections.