Kožuf mountain or Tzena (Greek: Τζένα/Tzena, Macedonian:  Кожуф планина ) is a mountain situated in the southern part of the Republic of Macedonia and partly in Greece. Its most western parts reach the river Blashnica, and the north-western side stretches in a line, from the Mrzhechko village via the village Konopishte, through the course of Boshava to the city of Demir Kapija. Kozuf is a specific mountain because it is the first natural barrier in the Republic of Macedonia that is directly exposed to the influences of the Mediterranean and the Aegean Sea. Its highest peak is Zelenbeg, at 2,171 meters above the sea level. A new and modern ski center was built recently on the mountain.