The Siege of Tripoli occurs in 1551 when the Ottomans besiege and vanquish the Knights of Malta in the fortress of Tripoli, modern Libya.

The Spanish had established a fort in Tripoli in 1510, and Charles V had remitted it to the Knights in 1530.

The siege culminates in a six-day bombardment and the surrender of the city onAugust 15.

The siege of Tripoli succeeds an earlier attack on Malta in July, which is repelled, and the successful invasion of Gozo, in which five thousand Christians captives were taken and brought on galleys to the location of Tripoli.