Two Molotov cocktails were thrown at the offices of Popular Orthodox Rally (LAOS) in Patissia, central Athens, on Friday night.
The attack cause minor damage to the partyís offices.
Nobody was hurt.
Ultranationalist LAOS surprised experts by gaining 2.7 percent of the vote in the European Parliament elections.
Although this did not lead to the party led by Giorgos Karatzaferis electing an MEP, it was a marked improvement on the 1.6 percent it received in the June 2012 national elections.