Police detained three people at the demonstration in and around the Paseo Ahumada pedestrian thoroughfare, witnesses said late Monday.
Around 500 people chanting anti-Pinochet slogans marched through the streets in anger at the decision, which effectively ended efforts to try Pinochet for human rights abuses.
The Appeals Court ruled that Pinochet, 85, suffers from such severe dementia that he cannot be prosecuted on charges of covering up 75 murders by the «Caravan of Death,» an army unit that killed suspected leftists.
It was the focus of Chilean efforts to prosecute Pinochet, who ruled the South American country from 1973 to 1990. Human rights campaigners said Chile had failed to live up to promises made abroad to try Pinochet for the killings or «disappearances» of more than 3,000 people.
Pinochet supporters contend that he should be praised for saving the nation from communism, and they welcomed the court ruling. President Richard Lagos urged Chileans to accept the controversial ruling without protest, CNN reported.