Protestors clashed with police, who fired tear gas early on Wednesday, several hours before the Greek parliament was to vote on an austerity package.
The vote on a 28.4 billion-euro ($40.8 billion) package of taxes, spending cuts and sell-offs is crucial for Greece to secure international aid to stave off bankruptcy, which is threatening the stability of the eurozone.
Police drove back a group of 400 leftwing demonstrators in front of the Hilton hotel in central Athens, who were making their way towards Syntagma square, where parliament is located, and dispersed them with tear gas.
Angry workers on Tuesday launched a 48-hour general strike, which brought about blanket power cuts and ground transport in the capital to a halt.
Lawmakers were due to begin voting on Wednesday afternoon on the austerity measures that would unblock 12 billion euros of emergency loans from last year's 110-billion bailout.
That would then free eurozone finance ministers to start drawing up a second bailout in talks in Brussels on Sunday.