Year 903 (CMIII) was a common year starting on Saturday of the Julian calendar.

• King Berengar I of Italy proceeds to issue concessions and privileges to the Lombard nobility and monasteries. He grants concessions to Bobbio Abbey in Emilia-Romagna (Northeast Italy).
• King Louis IV ("the Child") promulgates the Raffelstetten customs regulations, a legal document for a toll-bridge on the Danube River in Asten (modern Austria).

• The Danish Vikings invade Anglesey after being driven out of Dublin (see 902). They fail to gain a foothold in Wales, and sail on to Chester.
• A party of Danes under the Viking warlord Ingimundr attack the Welsh in a pitched battle at Maes Ros Meilon, perhaps near Llanfaes.

• November 29 – Battle of Hama: Abbasid forces under Muhammad ibn Sulayman al-Katib defeat the Qarmatians near Hama, on the banks of the Orontes River (modern Syria). The Qarmatian army is scattered and pursued by Abbasid troops; Al-Husayn ibn Zikrawayh and other Qarmatian leaders are captured.

• July – Pope Benedict IV dies after a 3-year reign. He is succeeded by Leo V as the 118th pope of the Catholic Church. Leo is imprisoned and tortured by Antipope Christopher after a reign of just 1 month. Christopher makes himself the new pope of Rome.

• December 7 – Abd al-Rahman al-Sufi, Persian astronomer (d. 986)
• Feng Yanji, chancellor of Southern Tang (d. 960)
• Kūya, Japanese priest of Pure Land Buddhism (d. 972)
• Li Gu, chancellor of Later Zhou (d. 960)
• Wang Jun, chancellor of Later Zhou (or 902)

• March 6
  • Lu Guangqi, Chinese official and chancellor
  • Su Jian, Chinese official and chancellor
• March 26 – Sugawara no Michizane, Japanese politician and poet (b. 845)
• June 10 – Cheng Rui, Chinese warlord
• July 27– Abdallah II of Ifriqiya, Aghlabid emir
• July – Benedict IV, pope of the Catholic Church^[1]
• December 24 – Hedwiga, duchess of Saxony
• December 30 – Tian Jun, Chinese warlord (b. 858)
• Adalhard of Babenberg, Frankish nobleman
• Moses Bar-Kepha, Syriac bishop and writer
• Théodrate of Troyes, Frankish queen (b. 868)
• Zhu Yanshou, Chinese governor (b. 870)