Ten separate marches converged on the capital's central Colon Plaza in a demonstration that was peaceful but gave the government an earful about the wage and pension cuts government workers face.
One teacher told CNN staff cuts at his school had inflated class sizes to the point that some students have to stand in class because there were not enough chairs in the classroom.
Despite an unemployment rate near 25 percent, Spain has had to implement even further spending cuts to secure international loans that would slash the national budget deficit.
Marchers claimed civil servants and other government workers were bearing the brunt of the cutbacks through no fault of their own. But the national government said the fiscal pain was necessary to get the Spanish economy back on track, the BBC said.
"These sacrifices are absolutely unavoidable if we are to correct the difficult economic climate we are experiencing," Economy Minister Luis de Guindos said. "We are laying the foundations for a recovery."