Year 1338 (MCCCXXXVIII) was a common year starting on Thursday (link will display the full calendar) of the Julian calendar.
Hundred Years' War: Louis IV, Holy Roman Emperor appoints Edward III of England as a vicar-general of the Holy Roman Empire. Louis supports Edward's claim to the French throne under the terms of the Treaty of Koblenz.
Philip VI of France besieges Guienne in Southwest France and his navy attacks Portsmouth in England.
Ashikaga Takauji is granted the title of Shogun by the emperor of Japan, starting the Ashikaga shogunate.
Nicomedia is captured by the Ottoman Empire.
January 13 – Jeong Mong-ju, Korean civil minister, diplomat and scholar (d. 1392)
January 21 – Charles V of France (d. 1380)
February 3 – Joanna of Bourbon (d. 1378)
March 23 – Emperor Go-Kōgon of Japan, a Northern Court emperor during a conflict between two imperial lines (d. 1374)
October 5 – Alexios III of Trebizond (d. 1390)
November 29 – Lionel of Antwerp, 1st Duke of Clarence (d. 1368)
date unknown
George de Dunbar, 10th Earl of March (d. 1420)
Muhammed V, Sultan of Granada (d. 1391)
Niccolò II d'Este, Marquis of Ferrara (d. 1388)
Thomas de Ros, 4th Baron de Ros (d. 1383)
Margaret de Stafford (d. 1396)
Tvrtko I of Bosnia (d. 1391)
April 8 – Stephen Gravesend, Bishop of London
April 24 – Theodore I, Marquess of Montferrat (b. c. 1270)
May – John Wishart, Scottish bishop
May 5 – Prince Tsunenaga, son of the Japanese Emperor (b. 1324)
June 10 – Kitabatake Akiie, Japanese governor (b. 1318; died in battle)
July – Muhammad Khan, Persian monarch
August 4 – Thomas of Brotherton, 1st Earl of Norfolk (b. 1300)
August 17 – Nitta Yoshisada, Japanese samurai (b. 1301; died in battle)
August 22 – William II, Duke of Athens (b. 1312)
December 21 – Thomas Hemenhale, Bishop of Worcester
date unknown
Alfonso Fadrique, Sicilian noble
Awhadi Maraghai, Persian poet
Marino Sanuto the Elder, Venetian statesman and geographer (b. c. 1260)
Nitta Yoshiaki, Japanese samurai
probable – Prince Narinaga, Japanese Shogun (b. 1325)
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