May 20 - Eastern Orthodox Church calendar - May 22

All fixed commemorations below celebrated on June 3 by Orthodox Churches on the Old Calendar.^{[note 1]}

For May 21st, Orthodox Churches on the Old Calendar commemorate the Saints listed on May 8.

• Holy Equals-to-the-Apostles Emperor Constantine (337), and Empress Helena, his mother (327)^{[1][2][3][note 2]}
• Martyrs Polyeuctus, Victorinus, and Donatus, at Caesarea in Cappadocia.^[5][6]
• Hieromartyr Secundus and those with him, in Alexandria (356)^[2][3][5]
• Saint Adelphios, Bishop of Onouphis, in Byzantine Egypt (c. 362, or c. 431)^{[7][note 3]}
• Saint Boros, monk.^{[8][note 4]}
• Saint Christopher I, Patriarch of Antioch (967)^[9]

• Hieromartyrs Timothy, Polius and Eutychius, deacons, in Mauretania Caesariensis (Morocco).^[5][10][11]
• Hieromartyr Valens and Companions, Bishop who was martyred in Auxerre in France along with three children.^[5][11]
• Martyr Secundinus, in Cordoba in Spain under Diocletian (c. 306)^[5][11]
• Saint Hospitius the Hermit of Nice, Wonderworker (581)^{[2][3][5][11][12]}
• Saint Barrfoin (Bairrfhionn, Barrindus) of Killbarron (6th century)^{[11][note 5]}
• Saint Gollen (Collen, Colan) of Denbighshire, a saint who has given his name to Llangollen in Wales (7th century)^[11]
• Saint Isberga (Itisberga) of Aire, reputed sister of Charlemagne, nun at Aire (Aria) in the Artois, of which she is the patroness (c. 800)^[11]
• Saint Ageranus (Ayran, Ayrman) of Beze, a monk at Bèze in France, martyred by the Vikings (888)^[11]
• Saint Theobald (Thibaud), Archbishop of Vienne (970-1001)^[11]

• Blessed Constantine (Yaroslav), prince, and his children Michael and Theodore, Wonderworkers of Murom (1129)^[2][3][13]
• Saint Cyril II (Kirill), Bishop of Rostov (1262)^[2][14][15]
• Saint Basil of Ryazan, Bishop (1295)^{[2][3][16][note 6]}
• Saint Helen of Decani, Serbia, Princess (c. 1350)^[2][3][17]
• Venerable Cassian the Greek, monk of Uglich, Wonderworker (1504)^{[2][3][18][19]}
• Saint Agapitus of Markushev (Vologda) the Hieromartyr, Abbot (1584)^[2][3][20]
• Saint Constantine the Fool-for-Christ, of Novotorzanin, Russia (c. 16th century)^{[21][note 7]}
• New Martyrs King Constantine Brancoveanu of Wallachia and his four sons Constantine, Stephen, Radu, and Matthew, and his counsellor Ianache (1714)^{[22][note 8]}
• Martyr Pachomios of Patmos (1730)^[3][23]

• Uncovering of the relics (1998) of St. Andrew Ogorodnikov, fool-for-Christ of Simbirsk (1841)^[2]
• Repose of Elena Pavlova of Chepel, Kharkiv (1885)^[2]
• Repose of Elder Isaac of Dionysiou Monastery of Mount Athos (1932)^[2]
• The Anastenaria fire-walking ritual is performed from May 21–23 in some villages in Northern Greece and Southern Bulgaria, coinciding with the feast of Constantine and Helen.^{[25][note 9]}
• Synaxis of all saints of Karelia,^[26]

• Sts Constantine and Helena, Holy Equals-to-the-Apostles.
• Sts Constantine and Helena, Holy Equals-to-the-Apostles (Mosaic in Saint Isaac's Cathedral, St. Petersburg, Russia).
• Stained glass window ( 1986 ) showing St Collen (Llangollen, Wales - St.Collen parish church)
• Icon of the Saints of Murom.
• King Constantin Brâncoveanu of Wallachia, and his sons (Church mural in Hurezi Monastery).
• “Vladimir” Icon of the Most Holy Theotokos.
• Mosaic icon of the Virgin of Tenderness, with the eponym "Episkepisis"("The Visitation"). From Triglia in Asia Minor, Church of Saint Basil (late 13th century)