Greek National Road 3 (Greek: Εθνική Οδός 3, abbreviated as EO3) is a single carriageway road in Greece. It connects Eleusis near Athens with the border of the Republic of Macedonia at Niki. It passes through Larissa and Florina. At Niki it connects with the M5K motorway to Bitola. Greek National Road 3 is one of the longest highways in Greece and up until the 1960s it served as the main route from Larissa to Thessaloniki. The new A1 motorway now offers a faster connection to Thessaloniki. Most of the EO3, except the southernmost section between Eleusis and Bralos, is part of the E65.
Throughout the late 1980s, motorway bypasses were constructed at the towns of Tyrnavos and Elassonas, but in 2002 plans surfaced to convert all of the road into a new motorway, from Larissa to Kozani and further on to Bitola, in the Republic of Macedonia. Throughout the 2000s motorway sections were delivered to the public and are running north of Larissa and north of Kozani, up to Ptolemaida. Remaining parts have either fallen through, as no construction works are currently being undertaken and no further announcements have been delivered by the government.