| Yahya III يحيى الثالث بن القاسم | |
| Succession: | Emir of Morocco |
| Reign: | unknown–905 |
| Full Name: | Yahya ibn al-Qasim |
| Predecessor: | Ali II ibn Umar |
| Successor: | Yahya IV ibn Idris |
| Dynasty: | Idrisid |
| Father: | al-Qasim ibn Idris |
| Birth Date: | unknown |
| Death Date: | 905 |
| Religion: | Islam |
Yahya III ibn al-Qasim (Arabic: يحيى الثالث بن القاسم) was an Idrisid ruler of Morocco.
Yahya was the son of al-Qasim, a younger son of the second Idrisid ruler of Morocco, Idris II . The family of al-Qasim controlled northern Morocco, with the cities of Tangier, Basra and Ceuta, and for a time in the 860s even the western half of the Idrisid capital, Fes.
Known by the sobriquet al-Miqdam, Yahya was called upon for assistance by the inhabitants of the Qaraqiyyin quarter of Fes when the town was occupied by the Kharijite rebel Abd al-Razzaq. Yahya drove the rebels away, and is traditionally accounted as the eighth Idrisid emir, until his death in 905.
Modern historians on the other hand consider that his rule over Fes is unlikely to have lasted long: his uncle, Dawud, appears to have ruled the city in 877, while numismatic evidence shows that between 880 and 893 the capital was ruled by members of a different branch of the Idrisid dynasty, descending from another uncle, Isa.
Yahya fell in battle in 905 against the forces of a cousin from a different branch of the dynasty, Yahya IV.