Dionysiou Monastery (Greek: Μονή Διονυσίου) is an Eastern Orthodox monastery at the monastic state of Mount Athos in Greece, at the southwest part of the Athos peninsula.

It is one of the twenty self-governing monasteries in Athos, and it was dedicated to John the Baptist.

The monastery is named after Saint Dionysius of Korisos [bg], who founded it in the 14th century.

Dionysius' brother was the metropolitan of Trebizond, whose ruler Alexios III Komnenos was the main benefactor of the monastery during its founding.

A passage from the chrysobull states that:[1] For all emperors, kings, or rulers of note have built monasteries on Mount Athos for their eternal memory; and since the emperor of Trebizond surpasses many of them, he too should add a new foundation in order to live eternally in the memory of the people and to enjoy unending pleasures of the soul.By the end of the 15th century, the Russian pilgrim Isaiah confirms that the monastery was Serbian.