Dionysiou Monastery is an Eastern Orthodox monastery located on the eastern side of Mount Athos in Greece. It is one of the twenty monasteries that make up the monastic community on Mount Athos, a UNESCO World Heritage Site.

The monastery was founded in the 14th century by St. Dionysius of Glushitsa, who was also its first abbot. The main church of the monastery is dedicated to the Virgin Mary and was built in the 16th century. The church is decorated with frescoes and icons from the 16th and 17th centuries.

Dionysiou Monastery has a rich collection of manuscripts and books, some of which date back to the 9th century. The monastery also has a collection of icons and religious relics, including pieces of the True Cross and the Holy Crown of Thorns.

The monastery is surrounded by a wall and has several towers, including the tower of St. Michael, which dates back to the 14th century. The tower was built to protect the monastery from pirates and other invaders.

Dionysiou Monastery has been damaged several times throughout its history, including during the Greek War of Independence in the early 19th century and during World War II. It has since been restored and continues to be an active monastic community, with around 50 monks currently living there.