One police officer was injured after the thugs disguised wearing "carnival masks" launched "two or three" petrol bombs at Syriza's Athen's base, according to authorities.
They targeted the building's entrance and two parked cars outside, causing slight damage.
Thirty-five suspects have been detained for questioning after Sunday's attack, which was described as "murderous" by a senior Syriza figure.
Central committee secretary Panayiotis Rigas, however, added the attack was carried out by criminal thugs and wasn't politically or ideologically motivated.
The headquarters of Greece's left-wing ruling party was attacked with petrol bombs
The building survived with minor damage, with blackened walls and chips in window panes, as well as, two cars also destroyed in the attack.
Opposition parities have stepped up their criticism for Syriza, they blame the government for lax policing after recent attacks targeting busses and ticket machines.
They accuse the ruling party of protecting the people who commit the attacks.
Syriza have been targeted by numerous protests, as the Greek government struggles to avoid bankruptcy.
Greek citizens have taken more than £2billion our of their bank accounts in just 45 days as they fear the economy is set to crash.
The nation now faces running out of money in just five months as it faces repayments of more than £5.1bn (€6bn) which they will be unable to achieve without help or restructuring.
The International Monetary Fund has warned Greece must agree a deal with creditors as soon as possible amid fears their debt crisis could damage the eurozone further.
In addition the IMF want EU countries to write off some of their loans in a bid to stop its debts spiralling out of control again.
Protest in Greece turns violent Wed, November 16, 2016
Protests in Greece turn violent following a protest against the visit of the US president in Athens on November 15, 2016
Play slideshow 1 of 34
Greece is hoping for an easier repayment deal on its £280billion debt pile which has been described by the IMF as "unsustainable and explosive".
There has been a discussion about allowing Greece to leave the eurozone, however Martin Schulz believes letting them leave is "absolutely negligent".
A total of 53 per cent of Greeks believed joining the currency was "wrong" for the country and have called for a return to the drachma.
- GREECE IN PANIC: Citizens withdraw £2.1bn from banks in 45 DAYS
- ‘Greece is on the right path’ Germany denies ‘GREXIT’ threat
- The Greeks needs 'LESS in emergency loans than originally agreed'