Year 302 (CCCII) was a common year starting on Thursday of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantius and Valerius or, less frequently, year 1055 Ab urbe condita. The denomination 302 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.

• Emperor Diocletian persecutes the Manichaeans, accusing them of being a Persian fifth column.^[1]
• Caesar Galerius wins his second victory over the Carpi.
• An invasion of Gaul by the Alemannic Lingones almost traps Caesar Constantius I between the enemy and the walls of a town. Constantius himself is carried onto the wall via a crane. However, within the same day, Constantius sallies forth from the walls and defeats the enemy in a major battle.

• Narseh, ruler (Shahanshah) of the Sassanid Empire, dies after a 9-year reign. He is succeeded by his son Hormizd II.

• Iamblichus of Chalcis writes a treatise on magic and the occult.

• Gregory the Illuminator is consecrated as Patriarch of Armenia by Leontius of Caesarea.

• Sun Sheng (or Anguo), Chinese historian (d. 373)

• Cao Huan, Chinese emperor of the Cao Wei state (b. 246)
• Narseh (or Narses), ruler of the Sassanid Empire
• Sima Jiong (or Jingzhi), Chinese prince and regent