Year 375 (CCCLXXV) was a common year starting on Thursday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year after the Consulship of Augustus and Equitius (or, less frequently, year 1128 Ab urbe condita). The denomination 375 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

• November 17 – Emperor Valentinian I concludes an enduring peace with the Alamanni in Germany, then marches into Illyrium to repel an invasion of the Quadi and the Sarmatians on the Danube frontier. While negotiating with the Quadi, Valentinian, age 54, becomes so enraged that he dies in a fit of apoplexy at Brigetio (Hungary). Extreme cruelty marked his 11-year reign, but he also founded schools and provided physicians to serve the poor of Constantinople.
• The Quadi accept an uneasy peace, Merobaudes (Magister militum), gives them land to settle on the Danube.
• Gratian, age 16, takes over the government at Augusta Treverorum (modern Trier), but ministers wishing to retain the loyalty of the Illyrian army and fearing a usurper. They proclaim Valentinian's 4-year-old son Valentinian II co-emperor with his mother, Justina, as regent. Gratian reserves for himself the administration of the Gallic provinces, and hands over Italy, Illyrium, Hispania and Africa to his stepmother, who makes Mediolanum (Milan) her residence.
• Gratian, advised by his chief advisor Ambrosius, begins a systematic presecution of the pagans. He confiscates the fortunes of the temples and adds the money to the Imperial Treasury. He procribes Arianism and Donatism.
• In Africa, the dissident Berber prince Firmus is delivered to the Romans by his brother Gildon.

• Emperor Chandragupta II becomes ruler of the Gupta Empire (India). He is the son of Samudragupta the Great and attaines his reign by an aggressive expansionist policy.

• The earliest extant books – a school textbook and an account book – with bound wooden leaves, are lost at the Dakhla Oasis in western Egypt. The desert sands preserve them for modern archaeologists.

• The first two Korean Buddhist temples are built.
• Saint Jerome retires to the desert of Chalcis (Syria).
• The Maronite Church is founded by Saint Maron in Lebanon.
• The Talmud of Babylon is written by Rav Ashi. This commentary on the Mishnah contains approximately 2.5 million words on 5.894 pages.

• Orosius, Christian historian and theologian (approximate date)

• Geunchogo, king of Baekje (Korea)
• Kipunada, king of the Kushan Empire (India)
• Rav Papa, Jewish amora and talmudist
• Samudragupta, emperor of the Gupta Empire
• November 17 – Valentinian I, Roman Emperor (b. 321)
• Wang Meng, prime minister of the Former Qin (b. 325)