List of state leaders in 303

302 state leaders - Events of AD 303 - AD 304 state leaders - State leaders by year

Asia

• Armenia - Tiridates III, King of Armenia (283–344)
• China (Western Jin Dynasty) - Emperor Hui, Emperor of China (290–307)
• Gupta Empire – Ghatotkacha, Gupta Emperor of India (280–319)
• Japan (Ancient period) - Emperor Ōjin, emperor of Japan (c.270-c.310)
• Korea (Three Kingdoms Period)
  • Baekje - Bunseo, King of Baekje (298–304)
  • Goguryeo - Micheon, King of Goguryeo (300–331)
  • Silla - Girim, King of Silla (298–310)
• Kushan Empire – Vasudeva II, Emperor of the Kushans (c.290–310)
• Western Kshatrapas - Vishwasen, King of the Western Kshatrapas (294–304)

Europe

• Western Roman Empire
  • Maximian, Western Roman Emperor in Italy and Africa (286–305)
    • Constantius Chlorus, Caesar in Spain, Gaul and Britain (293–305)

Middle East

• Eastern Roman Empire
  • Diocletian, Eastern Roman Emperor in the Orient (286–305)
    • Galerius, Caesar in Illyria, Macedonia and Greece (293–305)
• Persia (Sassanid Dynasty)
  • Hormizd II, Great King of Persia (302 - 309)