Montemassi is a village in Tuscany, central Italy, administratively part of the comune of Roccastrada, in the province of Grosseto.

It is located on a hill about 140 m (460 ft) above sea level.

In 1328 it was conquered by the condottiero Guidoriccio da Fogliano, fighting for Siena; the event is depicted in a famous fresco in the Palazzo Pubblico of Siena.

In the mid-16th century it became part of the Grand Duchy of Tuscany, following its history thenceforth.

It features a large polygonal rocca and a line of walls.