Fabio Orsini (1476 - 29 December 1503) was an Italian condottiero and lord of Mentana.

[1] He was son of Paolo Orsini,[2] a condottiero in service to the Papal States who was murdered in 1503 by Cesare Borgia.

[3] Following his involvement in the Magione conspiracy against Cesare Borgia, Paolo Orsini was arrested and Fabio fled.

[4] The following year, Fabio Orsini and Ludovico of Pitigliano returned with 400 horse and 500 foot soldiers to challenge Cesare,[5] but an alliance between the Borgia and the Colonna families allowed Cesare to prevail, and on 24 August Ludovico was defeated, forcing Fabio to flee once again.

[6] Fabio eventually died of a head wound on 29 December 1503, while fighting in the service of the Kingdom of Spain at the battle of Garigliano.