Umm al-Hajjaj bint Muhammad () was the famous principal wife of the ninth Umayyad caliph Yazid II and mother of eleventh Umayyad caliph Al-Walid II.
Her full name was Umm al-Hajjaj bint Muhammad ibn Yusuf al-Thaqafi, she belonged to Thaqafi tribe.
Yazid established marital ties to the family of al-Hajjaj ibn Yusuf (d. 714), the powerful viceroy of Iraq for his father, Caliph Abd al-Malik, and brother, al-Walid I (). He married al-Hajjaj's niece, Umm al-Hajjaj, the daughter of Muhammad ibn Yusuf al-Thaqafi. During her uncle's lifetime, she gave birth to Yazid's sons: al-Hajjaj, who died young, and al-Walid II, who became caliph in 743.
Umm al-Hajjaj became very influential wife of Yazid II. Her second son al-Walid, who was born in 709, was considered a candidate to the Caliphate throne.
Her husband, Yazid II died of tuberculosis in Irbid, a town in the Balqa subdistrict of Jund Dimashq (the military division of Damascus corresponding to Transjordan) on 24 Sha'ban 105 AH (26 January 724). His son al-Walid or half-brother Hisham led his funeral prayers. Yazid had intended to appoint al-Walid as his immediate successor but was persuaded by Maslama ibn Abd al-Malik to appoint Hisham ibn Abd al-Malik, followed by al-Walid.
Umm al-Hajjaj died during her husband reign or during her reign of brother-in law Hisham.