Protesters called for solutions to Spain's unemployment crisis, as well as protested against cutbacks in public funding, corruption amongst politicians and corporate greed, Think Spain reported.
Organizers with the 15-M movement said Saturday they planned to be in the streets all weekend.
On May 15 last year, a week before local and regional elections, protesters took to the streets and demand changes that would bring them some kind of hope for the future. At that time, protesters set up camps in city centers across Spain.
Spain's conservative government, led by Prime Minister Mariano Rajoy, has banned such camps this year, The Guardian reported.
The government's attempt to impose a 10 p.m. time limit for the protests Saturday failed, however, with people in Puerta Sol's city square at midnight Saturday.
Police moved into the camp and kicked people out between 2 a.m. and 5 a.m. Sunday, although many protesters had already left.
"The right to demonstrate has been combined with a lack of incidents and no camp-outs," the Interior Ministry said. "The police operation came to an end at 5 a.m. on Sunday after a calm day."
Protesting is expected to continue until Tuesday, with police presence increasing until then.