Marttila (Finnish: [ˈmɑrtːilɑ]; Swedish: S:t Mårtens, i.e. "Saint Martin's") is a municipality of Finland.

Marttila's neighbouring municipalities are Koski Tl, Lieto, Loimaa, Paimio, Pöytyä and Salo.

During the Swedish domestic war regarding who was to be king, an important battle took place here 29 August 1599.

Karl more or less already ruled Sweden and what is Finland nowadays, and Sigismund were based in Poland.

Martilla is along what at that time was called "Tavastlands Oxväg", in Finnish now posted as "Hämeen Härkätie", which in English translates to "Oxroad of Häme".