The siege of Balkh of 1525 saw the Uzbeks capture Balkh despite Babur's efforts to defend it. Balkh is around 150 miles to the north west of Babur's then capital of Kabul, on the border of the area he claimed in Afghanistan. Babur had fought off an attack on the city in 1517, before the start of his series of expeditions to India. Over the next few years he had crossed the Indus four times, and this may have encouraged the Uzbeks to attack Balkh.
The dates of the siege are not clear. Our only real clues come from Babur's own autobiography. We know that he left Kabul at the start of his fifth expedition to India in November 1525, his departure for India having been delayed by the need to lift the siege of Balkh.
We also know that he left Kabul for Balkh soon after giving Alam Khan, the uncle of Ibrahim Lodi, sultan of Delhi, permission to depart from Kabul for Delhi, and that this departure happened in hot weather in 931 A.H. (November 1524-October 1525).
This would suggest that the siege began in the spring or summer of 1525. It was lifted after Babur's arrival at Balkh, some time in the summer. The Uzbek leaders abandoned the siege to avoid fighting Babur, but the threat to the place didn't disappear. During his march into India over the winter of 1525-26 Babur was worried about Balkh, and the place appears to have been taken by the Uzbeks soon after this, for Babur described the place as having fallen to them because of the enfeeblement of the garrison by October 1525, and it appears to have remained in their hands for some time after this.