Year 1338 (MCCCXXXVIII) was a common year starting on Thursday of the Julian calendar.

• October 5 – Hundred Years' War, English Channel naval campaign: Southampton is destroyed.

• 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, England.
• Ashikaga Takauji is granted the title of shōgun by the emperor of Japan, starting the Ashikaga Shogunate.
• Nicomedia is captured by the Ottoman Empire.
• A Black Death plague strain originates near Lake Issyk-Kul in modern Kyrgyzstan, according to Syriac tombstone inscriptions and genetic material from exhumed bodies.^[1]

• January 13 – Chŏng Mong-ju, Korean civil minister, diplomat and scholar (d. 1392)
• January 21 – Charles V of France (d. 1380)^[2]
• February 3 – Joanna of Bourbon, queen consort of France (d. 1378)
• March 23 – Emperor Go-Kōgon of Japan, 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)
• May 23 – Alice de Warenne, Countess of Arundel, English noble (b. 1287)
• June 10 – Kitabatake Akiie, Japanese governor (b. 1318; d. 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; d. 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 shōgun (b. 1325)