Grammatiko (Greek: Γραμματικό) is a village in East Attica, Greece. Since the 2011 local government reform it is part of the municipality Marathon, of which it is a municipal unit.
Grammatiko is situated in the hills of the northeastern part of the Attica peninsula, 6 km from the South Euboean Gulf coast, at about 210 m elevation. It is 4 km southeast of Varnavas, 5 km north of Marathon and 32 km northeast of Athens city centre. The municipal unit Grammatiko consists of the villages Grammatiko, Agia Marina and Sesi.
Some wreckage from Helios Airways Flight 522 is reported to have fallen near Grammatiko on August 14, 2005.