The Saxon Eastern March or Ostmark is a march of the Holy Roman Empire from the 10th until the 12th century.

The term "eastern march" or "ostmark" comes from the Latin term marchia Orientalis and originally could refer to either a march created on the eastern frontier of the Duchy of Saxony or another on the eastern border of the Duchy of Bavaria: the Bavarian Eastern March, corresponding to later Austria.The Ostmark is created out of the vast Marca Geronis of Gero after his death in 965.

As Gero had died without issue his lands are divided by the establishment of the Northern March between the Elbe and Oder rivers, while the remaining Saxon Eastern March consists of the southern territory between Saale and Bóbr, roughly corresponding to the modern German Free State of Saxony.

Emperor Otto I invests Odo I with the title of a margrave.At the same time, the March of Meissen, the March of Merseburg and the March of Zeitz are created in the southern half of the Ostmark.