Ostmark (German: [ˈɔstmaʁk] ⓘ) is the name given to a currency denominated in Mark which was issued by Germany in 1918 for use in a part of the eastern areas under German control at that time, the Ober Ost area.

The currency consisted of paper money issued on 4 April 1918 by the Darlehnskasse in Kowno (Kaunas) and was equal to the German Papiermark.

The denominations available were: The reverse sides of the Darlehnskassenscheine carry a warning against forging banknotes in German, Latvian and Lithuanian.

The Ostmark and Ostrubel continued to circulate in Lithuania from the end of World War I until 1 October 1922, when they were replaced by the litas.

The reason for the replacement was the link to the Papiermark, which already suffered from inflation (and would spiral into hyperinflation in 1923).