Ostrubel (German and Polish: Ostrubel; Latvian and Lithuanian: Ostrublis; Russian: Острубль) is the name given to a currency denominated in copecks and rubels, which was issued by Germany in 1916 for use in the eastern areas under German occupation (Ober Ost and the Government General of Warsaw). It was initially equal to the Imperial rouble. The reason for the issue was a shortage of currency. The banknotes were produced by the Darlehnskasse in Posen (now Poznań) on 17 April 1916.

From 4 April 1916, the Ostrubel circulated alongside the Ostmark in the Ober Ost area, with 2 Ostmarken = 1 Ostrubel. In the Government General of Warsaw the Ostruble was replaced by the Polish marka on 14 April 1917.

The banknote denominations available were:

• 20 copecks;
• 50 copecks;
• 1 rubel;
• 3 rubels;
• 10 rubels;
• 25 rubels;
• 100 rubels.

The front sides of the banknotes carry a warning in German against forging banknotes. On the reverse sides is the same warning in Latvian (with old style orthography), Lithuanian and Polish.

There were also 1 copeck, 2 copeck and 3 copeck coins, made out of iron.

The Ostrubel circulated in Lithuania together with the Ostmark until 1 October 1922, when it was replaced by the litas.

It was also still in use in a part of the Second Polish Republic during the first months of independence, until 29 April 1920.