| Abu Muhammad Ubaydallah ibn Ahmad ibn Ma'ruf أبو محمد عبيد الله بن أحمد بن معروف | |
| Region: | Baghdad, Iraq |
| Era: | Islamic Golden Age |
| Parents: | Ahmad ibn Ma'ruf |
| Death Date: | 25 April 991 |
| Death Place: | Baghdad |
| Religion: | Islam |
| Creed: | Mu'tazilite (Sunni) |
| Main Interests: | Islamic theology, Islamic jurisprudence, Mu'tazilite creed |
| Office1: | Chief Judge of Baghdad, Iraq |
| Term Start1: | 18 July 967 |
| Term End1: | 970 Caliph: al-Muti |
| Term Start2: | 971 |
| Term End2: | 973/4 Caliph: al-Muti |
| Successor2: | Muhammad ibn Salih al-Hashimi |
| Office3: | Chief Judge of Baghdad |
| Term Start3: | 975 |
| Term End3: | 23 August 979 Caliph: al-Ta'i |
| Predecessor3: | Muhammad ibn Salih al-Hashimi |
| Successor3: | None (post vacant) |
| Office4: | Chief Judge of Baghdad |
| Term Start4: | 987 |
| Term End4: | 25 April 991 Caliph: al-Ta'i |
Abu Muhammad Ubaydallah ibn Ahmad ibn Ma'ruf (أبو محمد عبيد الله بن أحمد بن معروف) also known as Ubaydallah ibn Ahmad or simply as ibn Ma'ruf was thrice chief in Iraq for the Abbasid caliphs under the Buyid Emirs.
A Mu'tazilite, Ibn Ma'ruf was a prominent member of the cultural circle around the vizier Abu Muhammad al-Hasan al-Muhallabi (950/1–963).
On 18 July 967, Ibn Ma'ruf was appointed as of West Baghdad, the City of al-Mansur, and of the caliphal palaces. Abu Bakr Ahmad ibn Sayyar was his colleague as of the rest of East Baghdad except for March 968–January 970, when Ibn Sayyar took over responsibility for the entirety of East Baghdad.
Ibn Ma'ruf was appointed chief of Iraq in June 971 and held the office until he resigned in 973/4 in protest at the interference of the Buyid emirs in the administration of justice. His successor, Muhammad ibn Salih al-Hashimi, was deposed in May/June 975, and Ibn Ma'ruf was restored to the office of chief . Caliph al-Ta'i offered Ibn Ma'ruf the position of caliphal secretary, but Ibn Ma'ruf refused.
He was dismissed and exiled to Fars by the Buyid ruler Adud al-Dawla on 23 August 979, along with other members of the Baghdad establishment close to the caliph. The position of chief in Baghdad was abolished altogether, and the judicial administration of Iraq handed over to the chief of Shiraz. Iraq was thus effectively reduced to a regular province of the Buyid empire, governed from a new imperial centre.
Although Ibn Ma'ruf was released from captivity by Adud al-Dawla's successor, Sharaf al-Dawla, in 983, no chief was appointed in Baghdad until Ibn Ma'ruf's return in 987, when he resumed his position and held it until his death on 25 April 991.