It was first mentioned in historical documents in 860. The Spanheims, a noble family, bestowed the hereditary office of cupbearer to the Osterwitz family in 1209. The last Osterwitz innkeeper was captured during a Turkish invasion in 1475 and died in captivity without an heir. Ownership of Hochosterwitz fell back to the sovereign Emperor Friedrich III. King Ferdinand I pledged Osterwitz to the governor Christof Khevenhüller; in 1571, Georg Freiherr von Khevenhüller, also governor, purchased the castle, expanded it due to the threat of Turkish invasions, equipped it with an armory, and had 14 gates built from 1570 - 1586. Such a multifaceted, secured castle path is not only one of the greatest rarities but is also a unique feature in castle construction. An old document lists the names of the individual towers.
Since this time, no significant structural changes have occurred. The castle has been under the ownership of the Khevenhüller family to this day without interruption. According to a decree by owner Georg Khevenhüller from 1576, which can be read on a marble plaque in the courtyard, the castle should remain in the possession of descendants, who should take care of its preservation. The Khevenhüller family have always felt committed to this legacy.