Ostenk (; sometimes Ostenik) is a settlement in the Municipality of Trbovlje in central Slovenia. It lies in the hills northeast of the town of Trbovlje. Traditionally the area was part of the Styria region. It is now included with the rest of the municipality in the Central Sava Statistical Region. Ostenk is a scattered settlement on a ridge centered on the Ostenk Crest . It is bordered to the south by Ostenik Hill—which is also known as Žrebelj Hill (, literally 'nail hill') on the Hrastnik side.