Year 1366 (MCCCLXVI) was a common year starting on Thursday of the Julian calendar.

• March 13 – Henry II deposes his half-brother, Pedro of Castile, to become King of Castile.
• October 12 – Frederick III of Sicily forbids decorations on synagogues.
• October 26 – Comet 55P/Tempel–Tuttle passes 0.0229 AU (3,430,000 km; 2,130,000 mi) from Earth.^[1]

• War continues between the Hindu Vijayanagar Empire and the Muslim Bahmani Sultanate in modern-day southern India.
• Dmitri Donskoi, ruler of Moscow and Vladimir, makes peace with Dmitri Konstantinovich, former ruler of Vladimir.
• Abu Faris Abd al-Aziz I of Morocco succeeds assassinated Abu Zayyan as Sultan of the Marinid Empire in Morocco.
• The Statutes of Kilkenny are passed, aiming to curb the decline of the Hiberno-Norman Lordship of Ireland.
• The Den Hoorn brewery is founded at Leuven in the Low Countries. In 1717 this will be renamed the Brouwerij Artois, and later releases a beer in 1926 named Stella Artois.
• Zhu Yuanzhang, leader of the Red Turban Rebellion that will overthrow the Yuan dynasty and establish the Ming dynasty two years later, begins building the walls for a new capital city at Nanjing.
• Thomas Fraser obtains lands in Aberdeenshire (Scotland) on which he starts the building of a towerhouse, that will later be known as Muchalls Castle.

• May 11 – Anne of Bohemia, queen of Richard II of England (d. 1394)^[2]
• August 28 – Jean Le Maingre, marshal of France (d. 1421)
• date unknown
  • Lady Elizabeth FitzAlan, English noblewoman (d. 1425)
  • Miran Shah, governor of Azerbaijan (d. 1408)
• Approximate
  • Eleanor de Bohun, English noble (d.1399)^[3]

• January 25 – Henry Suso, German mystic (b. c. 1295)
• April 26 – Simon Islip, Archbishop of Canterbury
• May 20 – Maria of Calabria, Empress of Constantinople (b. 1329)
• Summer – Ming Yuzhen, founder of the rebel empire of Daxia (b. 1331)
• October 14 – Ibn Nubata, Arab poet (b. 1287)^[4]
• October 18 – Petrus Torkilsson, Archbishop of Uppsala