|738 by topic|
|Ab urbe condita||1491|
|Balinese saka calendar||659–660|
|Chinese calendar||丁丑年 (Fire Ox)|
3434 or 3374
— to —
戊寅年 (Earth Tiger)
3435 or 3375
|- Vikram Samvat||794–795|
|- Shaka Samvat||659–660|
|- Kali Yuga||3838–3839|
|Japanese calendar||Tenpyō 10|
|Minguo calendar||1174 before ROC|
|Seleucid era||1049/1050 AG|
|Thai solar calendar||1280–1281|
864 or 483 or −289
— to —
865 or 484 or −288
Year 738 (DCCXXXVIII) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. The denomination 738 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.
- Charles Martel, Merovingian mayor of the palace, begins a campaign against the Saxons (in modern-day Westphalia) on the northeast frontier. They are subdued and must pay him tribute.
- Kormesiy, ruler (khagan) of the Bulgarian Empire, is deposed by the nobility. He is replaced on the throne by his son Sevar, who is a descendant of the royal Dulo clan.
- Felice Cornicola is appointed hypatos (Byzantine consul) and magister militum of Venice.
- King Swæfberht of Essex dies after a 23-year reign. He is succeeded by Saelred, a minor member of the Essex royal family.
- The Mayan city-state Xukpi (Copán) is defeated by a rival city-state, Quiriguá. Xukpi leader Uaxaclajuun Ub'aah K'awiil ("Eighteen Rabbit") is deposed thereafter.
- Boniface visits Rome, and is made papal legate of the Frankish Kingdom. He establishes many bishoprics in Bavaria.
- Abu Yusuf, Arab jurist and chief adviser (approximate date)
- Chengguan, Chinese Buddhist monk (d. 839)
- January 26 – John of Dailam, Syrian monk (b. 660)
- May 3 – Uaxaclajuun Ub'aah K'awiil, Mayan ruler (ajaw)
- Áed mac Colggen, king of the Uí Cheinnselaig (Ireland)
- Asad ibn Abdallah al-Qasri, Arab governor
- Dluthach mac Fithcheallach, king of Uí Maine (Ireland)
- Fáelán mac Murchado, king of Leinster
- Maslama ibn Abd al-Malik, Arab general
- Suluk, Turkic ruler (khagan) of the Turgesh
- Swæfberht, king of Essex
- In the fiction of H. P. Lovecraft, Abd Al Azred, Muslim-kafir scholar and scientist, is killed in Damascus city market. His treatise on religion, the Al-Azif, is published soon thereafter.