The marches, organized by Spain's "indignados" protest movement, came after Cyprus announced it would dip into its citizens' bank accounts to help save the government from a debt default, part of a €10 billion ($13-billion) EU bailout deal.
"We don't owe anything. We won't pay anything," said a banner carried by protesters in the northern city of Valladolid, a rallying cry echoed at the march in Madrid.
"Get out Troika," protesters chanted in the capital, a reference to the trio of creditors — the EU, the European Central Bank and the International Monetary Fund — that are overseeing eurozone bailouts brought on by the debt crisis.
In Madrid, the protesters marched to Puerta del Sol, a central square that was occupied for several months by the indignados, whose movement was born in May 2011 and inspired Occupy protests in other countries.
Their slogans and banners covered a wide array of issues ranging from austerity cuts to corruption scandals to unemployment.
"We want to condemn the situation in Europe, where they save the bankers but make us all pay," said Teresa Partida, an unemployed 60-year-old woman."
"They're swindlers, thieves. They should be ashamed," said Begonia Crespo, a 52-year-old actress, condemning a scandal in which leaders of Spain's right-wing ruling party allegedly received envelopes stuffed with cash.
Spain has been hit hard by austerity measures imposed under pressure from the EU to get its accounts in order. The government is aiming for €150 billion in savings by the end of 2014.
It cut its deficit from 9.4 percent of gross domestic product in 2011 to 6.7 percent in 2012, but has been unable to cut its 26-percent unemployment rate or halt a grinding recession that saw the economy shrink 1.4 percent last year.