The Koutloumousiou Monastery (Greek: Μονή Κουτλουμουσίου) or Koutloumousi (Κουτλουμούσι) is an Eastern Orthodox monastery in the monastic state of Mount Athos in Greece. The monastery ranks sixth in the hierarchy of the Athonite monasteries.

Its was founded in the 11th century by Kallistos Koutloumous, an orthodox monk from the city of Iconium in Minor Asia. The first benefactor was the byzantine Emperor Alexios I Komnenos, who appreciated the piety of Kallistos and strengthened the Monastery.

The monastery was raised with the help of voivodes Nicolae Alexandru Basarab and Vladislav Vlaicu from Wallachia, while other Wallachian voivodes contributed with substantial financial donations (Mircea cel Bătrân, Laiotă Basarab, Basarab cel Tânăr, Vlad al IV-lea Călugărul, Vlad al VI-lea Înecatul, Vlad al VII-lea Vintilă, Radu cel Mare, Neagoe Basarab).

The monastery's library contains 662 manuscripts and approximately 3,500 printed books.

It has 26 working monks.

Koutloumousiou Bridge [bg] (Greek: Γεφύρι στην Ιερά Μονή Κουτλουμουσίου) connects Koutloumousiou Monastery with Karyes.

• George (Schaefer)
• St. Paisios of Mount Athos
• Father Christodoulos, who became Abbot of Koutloumousiou in 1975 after migrating with 8 monks from a monastery in Euboea

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  Koutloumousiou Monastery
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  Olive trees near the monastery
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  The church of the monastery
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  Courtyard detail

• Official website
• Koutloumousiou monastery at the Mount Athos website
• Greek Ministry of Culture: Holy Monastery of Koutloumousiou