Abul-Qasim Babur Mirza bin Baysonqor Beg (Chagatai/Persian: ابوالقاسم بابور میرزا بن بایسنقر بیگ), was a Timurid ruler in Khurasan (1449–1457). He was the son of Ghiyath-ud-din Baysonqor ibn Shahrukh Mirza, and thus a great-grandson of Amir Timur.
Babur was one of the many people involved in the succession struggle that took place during Shah Rukh's last years. Together with Khalil Sultan (a great-great-grandson of Timur), he plundered the baggage-train of the army and then made his way to Khurasan. Meanwhile, Ulugh Beg also invaded Khurasan in 1448 in an attempt to defeat Ala-ud-Daulah Mirza bin Baysonghor (علاء الدولہ میرزا بن بایسنغر), who held Herat. Ulugh Beg defeated Ala-ud-Daulah Mirza bin Baysonghor at Tarnab and took Mashhad, while his son Abdal-Latif Mirza conquered Herat. Ala-ud-Daulah Mirza bin Baysonghor fled to south-western Afghanistan. However, Ulugh Beg felt Transoxiana, where he had already ruled for decades, to be more important, and soon left the area. On the way back, Babur sent a force that inflicted heavy losses on his army.
With a power vacuum now in Khurasan, Babur quickly seized control. Mashad and Herat fell to him in 1449. Ala-ud-Daulah Mirza bin Baysonghor occasionally raided the area but was not a significant factor. Together with Ulugh Beg and Sultan Muhammad bin Baysonghor (سلطان محمد ابن بایسنغر ) (who gained control of central Persia), Babur became one of the three important Timurid rulers. This balance of power was soon upset by Sultan Muhammad bin Baysonghor, who invaded Khurasan. The campaign started out badly for Babur, with a defeat at Mashad in March 1450 convinced him to cede parts of his territory. However, Babur soon recovered and took Sultan Muhammad prisoner, and then executed him. He then marched to Shiraz to take control of Sultan Muhammad's lands.
At this point Jahan Shah of the Black Sheep Turkmen ended his loyalty to the Timurids. He quickly put Qum and Sava to siege. Babur began to march against him but was forced to return to Herat, due to the overwhelming superiority of the Black Sheep's armies and a plot hatched against him by 'Ala' al-Daula. Most of Persia was taken from the Timurids by 1452, with the exception of Abarquh, which was conquered by the Black Sheep in 1453. While Kirman was temporarily conquered some time later and a few attempts were made to seize Ray, Persia as a whole was never retaken by the Timurids.
In 1454 Babur invaded Transoxiana, then under the control of Abu Sa'id Mirza in retaliation for the latter's seizure of Balkh. He quickly laid siege to Samarkand. The conflict between the two soon ended, however, with the Oxus River agreed to as the border. This remained in effect until Babur's death in 1457. He was succeeded by his son Mahmud.