Hasištejn (German: Burg Hassenstein) is a ruined medieval castle in Bohemia, the Czech Republic. It is situated near Kadaň, Klášterec nad Ohří and Chomutov.
The castle, first mentioned in Maiestas Carolina, was probably founded by Friedrich of Schönburg to guard the way from Prague to Saxony. The castle was seized by Václav IV of Luxembourg and it was given to the house of Lobkovic.
The most renowned inhabitant was Bohuslav Hasištejnský z Lobkovic, a poet and traveller who was born in Hassenstein and lived there permanently from 1503 to his death in 1510. He gathered a huge library in the castle and a lot of humanists Like Martin Luther and Melanchthon came to visit Bohuslav. After his death the castle started to become desolate and caught fire in 1560. It still has a well-kept tower and walls.