Abu Sa'id Bahadur Khan (June 2, 1305 – December 1, 1335) (Persian, Arabic: ابو سعید بہادر خان ), also spelt Abusaid Bahador Khan, Abu Sa'id Behauder (Mongolian: ᠪᠦᠰᠠᠢ ᠪᠠᠬᠠᠲᠦᠷ ᠬᠠᠨ, Busayid Baghatur Khan, Бусайд баатар хаан/Busaid baatar khaan, [ˈbusæt ˈbaːtər xaːŋ] in modern Mongolian), was the ninth ruler of Ilkhanate c. 1316-1335. This kingdom encompasses the present day countries of Iran, Azerbaijan, Georgia, and Armenia, as well as portions of Iraq, Turkey, Afghanistan, and Pakistan.

After defeating the forces of Golden Horde and the rebellion groups of the Keraites Rinchin, in 1306 and 1322 respectively, the Mongols gave the title of Baghatur (from Mongolian "баатар", meaning "hero, warrior"), to the infant heir-apparent of Öljaitü, Abu Sa'id, who was born in Ujan.

During the earlier years of Abu Sa'id's reign, the Judeo-Muslim scholar and Vizier Rashid-al-Din Hamadani was beheaded. This left the emir Chupan as the de facto ruler of Ilkhanate. In 1325, Chupan defeated a force led by Muhammad Üzbeg, Khan of the Golden Horde. In turn, the emir Chupan invaded the Golden Horde's territories.

Abu Sa'id then fell in love with Baghdad Khatun, one of emir Chupan's daughters. The emir's efforts to keep Abu Sa'id from marrying his daughter, who was still married to Hasan Buzurg (another powerful kingmaker of the era), did not help the situation. In August 1327, Abu Sa'id had one of Chupan's sons, Demasq Kaja, killed, apparently for his activities with a former concubine of Öljaitü's. Later, Chupan himself was killed by the Kartids, who were the lords of Herat. In the meantime, the Mamluks beheaded Timurtash, another son of Chupan, who was a governor and had revolted against the Ilkhanate years before, and had shown unusual mercy.

In the 1330s, the outbreak of the Black Death ravaged the Ilkhanate. Abu Sa'id and his sons were among those who fell victims to the plague.^[2] In consequence of which, Abu Sa'id died without an heir or an appointed successor, thus leaving the Ilkhanate vulnerable, leading to clashes of the major families, such as the Chupanids, the Jalayirids, and new movements like the Sarbadars. On his return to Persia, the great voyager Ibn Battuta was amazed to discover that the realm which had seemed to be so mighty only twenty years before, had dissolved so quickly. The Ilkhanate lost cohesion after the death of Abu Sa'id, and that of his successor, Arpa Ke'un, becoming a plethora of little kingdoms run by Mongols, Turks, and Persians.

Abu Sa'id married six times:

Abu Sa'id had one daughter