| Abu Yahya Zakariya al-Musta'sim أبو يحيى زكريا المستعصم | |
|---|---|
| 8th Caliph of Cairo (first period) | |
| Reign | 1377 |
| Predecessor | al-Mutawakkil I |
| Successor | al-Mutawakkil I |
| (second period) | |
| Reign | 1386–1389 |
| Predecessor | al-Wathiq II |
| Successor | al-Mutawakkil I |
| Born | unknown date Cairo, Mamluk Sultanate (now Egypt) |
| Died | 1389 Cairo, Mamluk Sultanate |
| Father | al-Wathiq I |
| Religion | Sunni Islam |
Abū Yahya Zakariya al-Musta'sim bi'llah (Arabic: أبو يحيى زكريا المستعصم بالله; died 1389) was the eighth Abbasid caliph of Cairo under the tutelage of the Mamluk Sultanate. He served twice: first in 1377, then again in 1386–1389.
Al-Musta'sim was the son of al-Wathiq I (the fourth Caliph of Cairo). His given name was Zakariya and his Kunya was Abu Yahya. He was first installed in the office in 1377 for a short period of time, after al-Mutawakkil I was deposed. Al-Musta'sim was also deposed by Mamluk sultan and al-Mutawakkil I was again installed as caliph of Cairo by Mamluks.
After few years, in 1386 al-Musta'sim was again installed as caliph of Cairo for the Mamluk Sultanate. He remained in the office from 1386 to 1389 and he was again succeeded by al-Mutawakkil I in 1389.