Burg Oybin, Mountain castle ruins in Upper Lusatia, Germany.

Burg Oybin is a hilltop castle ruin on the 514-metre Oybin hill in the Žitavské hory, about two kilometres north of the Czech-German border. Its walls, the Kaiserhaus on the west side, the ruins of a Celestine monastery founded in 1369, a plateau cemetery and a restaurant hut occupy the whole summit, where a camera obscura also stands.

The castle first appears in records in 1291 as Moybin, when it was destroyed by the town of Zittau for sheltering robber knights. Charles IV built the Kaiserhaus in 1364 and founded the Celestine monastery in 1369; the monastery was dissolved after the Reformation and its property sold to Zittau in 1574. Lightning struck the church in 1577, starting the ruin's decay.

The ruins attracted German Romantic painters in the 19th century, who created numerous artworks capturing the sandstone structures set against mountain landscapes.

Access to the ruins follows marked hiking paths from Kurort Oybin village, with trails offering varying levels of difficulty for different visitors. Sturdy footwear is important since the rocky path becomes slippery when wet.

The site holds a camera obscura at the summit of the 514-metre hill, and the monastery ruin has served as a concert hall since 1972, used among other things for the traditional Mönchszug procession. A monument to historian Christian Adolph Pescheck stands in the castle grounds.