A strong 5-magnitude tremor hit just west of the Greek island of Kefalonia in the Ionian Sea in the early hours of Sunday.
The quake, which hit at 1.15am local time, had its epicentre five kilometres underwater, the Athens Geodynamic Institute reported.
There have been no immediate reports of damage or injuries.
A 4.7-magnitude quake had hit the island on Friday.
The area often produces very strong quakes. The island was flattened in 1953 by a 7.2-magnitude tremor.