Al-Khayzuran bint Atta (Arabic: الخيزران بنت عطاء, romanized: al-ḵayzurān bint ʿaṭāʾ) (died 789) was the wife of the Abbasid Caliph Al-Mahdi and mother of both Caliphs Al-Hadi and Harun al-Rashid. She maintained de facto influence from 775 to 789 during the reign of her husband and sons and is known for her immense influence on state affairs.

al-Khayzuran was not formally a ruler, but was nevertheless the first woman in the history of Islam to rule de facto and was the first woman in the history of Muslims to have gold coins in her name. She became one of the most powerful women of her time under the name of her husband and sons, al-Mahdi, al-Hadi and al-Harun. During the reign of al-Mahdi, al-Khayzuran often appeared at the court when the caliph was present and also used great political power, and caliph sought her views on most matters before issuing orders.

Al-Khayzuran was also the first woman to have her own bureaucracy and court and accept petitions and the audience of officials and the people, and to command and forbid in the caliphate. Independent of the state treasury, she gained enormous wealth by having extensive trade relations with other countries. While al-Mahdi spent most of his time hunting and having fun, she, by influencing the court, was able to hold meetings in her house to run the caliphate. Even after his death, she continued to wield premier power and influence during her sons' time.

At the time of al-Mahdi's untimely death, al-Khayzuran in the capital (Baghdad) had already taken over government affairs and by hiding his death and paying the salaries of army officers, she secured the allegiance of the soldiers for her son al-Hadi as the new caliph, but al-Hadi opposed his mother in sharing and partnership unquestionable power in the caliphate, and al-Khayzuran killed him after severe disputes. She brought Harun al-Rashid to power. Unlike his brother, al-Harun did not oppose his mother and officially handed over all power to his mother and relied upon his mother's advice.

Al-Khayzuran was born in Jorash, near modern Bisha, Saudi Arabia. She was kidnapped from her home by a Bedouin who then sold her in a slave market near Mecca to Al-Mahdi during his pilgrimage. Officially it was illegal for Muslims to enslave Muslims, however all sources are nevertheless adamant that she was a slave, and to break the official rule barring the enslavement of Muslims was not an unusual in practice in that context.

Al-Khayzuran was described as beautiful, intelligent and gifted. At that time the woman slaves of the harem, called jarya or jawari, were famed for educating themselves in music, singing, astrology, mathematics and theology in order to keep their master's interest, and Al-Khayzuran took regular lessons in fiqh from the most learned qadis.

She eventually became the favorite of Al-Mahdi. Upon his succession as caliph in 775, she convinced him to free and marry her; depriving his first wife, Princess Rayta (daughter of Caliph Al-Saffah) of her privileges as well as demoting her son from the position of heir to the throne. Instead, Al-Mahdi name Al-Khayzuran's sons as his heirs, despite the fact that it went against custom for the sons of a slave to be so named. As a queen, al-Khayzuran now held supreme authority over the caliph's harem; even the caliph had to behave in this area according to her wishes. She quickly took over the management of this complex institution, from social life to the planning of parties and ceremonies, including the management of the large sums of money that come in.

From that point on, she was the most powerful and influential woman in the empire, accompanying Al-Mahdi whenever he held court. She hidden behind a curtain, and if she did not agree with something, she would place her hand on his back out of sight. Al-Khayzuran had direct access to the caliph at all times: her suggestions were always adopted, individuals she recommended were favored and promoted, and at her intercession he forgave enemies or commuted death sentences.