Kozjak (pronounced [ˈkoːzjak], sometimes Kozjek,[2][3][4] German: Kosiek[2][3]) is a former village in eastern Slovenia in the Municipality of Trebnje.

Kozjek Hill (elevation: 456 meters or 1,496 feet) rises northwest of the settlement.

[6] On the summit of Kozjek Hill there are the ruins of a castle; it was mentioned in written documents in 1274 and it still stood in the 17th century, when it was acquired by the Auersperg family.

The Counts of Saurer, who shielded Protestants during the Reformation, were among the earlier owners of the castle.

[1][5] Kozjak was annexed by Dolenje Selce in 1955, ending its existence as a separate settlement.