The Monastery of St. Theodosius, also known as Deir Dosi and Deir Ibn Ubeid in Arabic, is a monastery founded around 476 by Saint Theodosius the Cenobiarch and that since at least the 12th century contains his (today empty) tomb. It is located within the village of al-Ubeidiya, some 8 kilometres east of Bethlehem, on the road towards Mar Saba (St Sabbas) Monastery, in the West Bank, Palestine.

A church of the Theotokos was built by Sophronius between 529-543, whose remains have been obliterated by the construction of the modern church.

The Byzantine monastery was destroyed in the first half of 7th century, during the Persian and Muslim conquests.

Ancient sources describe an attack by Arab troops on the monastery in 789, with churches being destroyed and monks being killed. This event is described as part of a series of such attacks against monasteries in Jerusalem and the Judean desert at the end of the 8th and beginning of the 9th century. Still, archaeology tends to paint a picture of peaceful abandonment, rather than destruction brought about by man or nature.

The monastery was rebuilt during the Crusader period.

Between 1113 and 1115 CE Abbot Daniel visited and noted: "Six versts from Jerusalem is the convent of St. Theodosius; it is located on a mountain; walls surround it. We see there, at the top of the mountain, in the enclosure of the convent, a cave which once served as a shelter for the night to the Magi, when they fled from Herod. This is where the relics of Saint Theodosius and several other holy fathers now rest, as well as those of his mother and the mother of Saint Saba."

The monastery survived and flourished well into the 14th century, but by 1400 it lay again in ruins. The Russian pilgrim Agrefeny described it as in ruins when he passed it around 1370. Two 15th-century pilgrims describe it as first used by Muslims for stalling cattle, and later as ruined.

In 1863, Victor Guérin visited the place, which he called Deir Dôsi, and noted:

The remains of the monastery of St. Theodosius consist of vaults and sections of walls built with stones of different sizes, some of which appear to come from ancient buildings. The location of two churches is very recognizable. One, which has now been converted into an area ["aire" in French; flat surface?], was paved with large mosaic cubes, as evidenced by numerous samples still scattered on the ground. This edifice is, moreover, almost entirely razed to the ground. Rectangular in shape, it faced west to east.

Of the other site he noted:

The second church, also shattered from top to bottom, has nonetheless suffered far less destruction than the other. It contained a crypt now half buried under piles of rubble. This crypt, if we are to believe a very ancient tradition, would have been originally a natural cave where the Magi supposedly took shelter, when, after having adored the infant Jesus in Bethlehem, they returned by another route to their country.

The site of the old monastery was prepared for reconstruction by the Greek monks of the Jerusalem Church in 1898 and the compound was gradually rebuilt during the 20th century.

In 1898 Conrad Schick noted that "the ruins are [..] those [..] of a former convent, and only in modern times used as a storehouse for grain by the wandering tribe Ubedieh. Now it seems the Greek convent in Jerusalem had some rights of property in this place, and, having made an agreement with the Arabs to quit it, took possession of it last year. They began to remove the débris, and so laid bare the remaining walls, &c., and have begun to build it up again. The laying of the foundation stone, or a kind of resanctifying of the place, was celebrated in a grand manner and before a crowd of people. [..] The monastery will be restored, and again become a station for pilgrims visiting Mar Saba..."

A cave on the monastery grounds is, according to tradition, the place where the three Magi took shelter during the first night after delivering their gifts to the newborn Baby Jesus, after an angel had appeared to them and ordered them to return home without reporting Jesus' location to King Herod. This Cave of the Magi is called Metopa in Greek.

The cave was used during the Byzantine period as a cemetery. Important monastic figures of Palestine buried here include several saints, such as John Moschus, buried here by Sophronius of Jerusalem; Saint Sophia, the mother of Saint Sabbas the Sanctified; Saint Theodota, the mother of the Holy Unmercenaries Cosmas and Damian, etc.

• Greek Orthodox Patriarchate of Jerusalem: The Holy Monastery of Saint Theodosius the Cenobiarch (the saint's vita and the story of his monastery)
• AtlasTours.net: St. Theodosius Monastery, Bethlehem
• The Official Website for Tourism in Palestine: St. Theodosius Monastery
• EWTN Global Catholic Network Archived 2016-06-01 at the Wayback Machine (Eternal Word Television Network, Irondale, Alabama): St Theodosius, the Cenobiarch (A.D. 529)