Year 738 (DCCXXXVIII) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar, the 738th year of the Common Era (CE) and Anno Domini (AD) designations, the 738th year of the 1st millennium, the 38th year of the 8th century, and the 9th year of the 730s decade. 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.

• 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.