Aistulf, also called Aistulf of Friuli, (d. 756) was king of Lombards (749-756) and duke of Spoleto (751-756).

After he succeded Ratchis as the king of Lombardy in 749, Aistulf continued the policy of expansion and raids against popes and the Byzantine exarchs of Italy. In 751, he captured Ravenna. He even threatened Rome itself, and claimed a capitation tax.

The popes, thoroughly irritated and alarmed, and hopeless of aid from the Byzantine empire, turned to the Carolingian mayors of the palace of Austrasia, the effective rulers of the Frankish kingdom. In 741, pope Gregory III asked Charles Martel to intervene, but he was to busy elsewhere and declined. In 753, pope Stephen III visited Charles Martel's son Pippin the Short, who had proclaimed himself king of the Franks in 751. In return for the transfer by the pope of the Frankish crown from the decayed line of Clovis to his own, Pippin crossed the Alps, defeated Aistulf and gave to the pope the lands which Aistulf had torn from the empire.

Aistulf died hunting in 756. He was succeded by Desiderius as king of Lombardy and by Alboin as duke of Spoleto.