Abu'l-Hasan Ali ibn Fadl ibn Ahmad Isfaraini (Persian: ابوالحسن علی بن فضل بن احمد اسفراینی, died 1013/4), better simply known as Abu'l-Hasan Isfaraini (ابوالحسن اسفراینی), was a Persianvizier of the Ghaznavid Sultan Mahmud of Ghazni (r. 998 – 1030) from 998 to 1010.
He was probably from Isfarain in northwest Khurasan. Not much is known about his early life; he began his career as a Samanid secretary (dabir) under the Turkic slave-general Fa'iq. During this period the Samanid dynasty was in heavy decline and was struggling for holding control over Khurasan and Transoxiana from several ambitious military leaders who had rebelled against their authority, the most dangerous ones being Fa'iq and the Simjurid Abu 'Ali Simjuri.
The Ghaznavid prince and Samanid general Sebüktigin, however, managed to defeat the rebels, but soon took control over Khurasan, while the remains of the Samanid dynasty in Bukhara was conquered by the Kara-Khanid Khanate. Isfaraini shortly changed his allegiance to the Ghaznavids, where he rose to prominent offices. In 997, Sebüktigin died and was succeeded by his son Ismail, who soon, however, was defeated by his brother Mahmud, who crowned himself as the new ruler of the Ghaznavid dynasty, and shortly appointed Isfaraini as his vizier, thus making Isfaraini become the first vizier of the Ghaznavid dynasty. Isfaraini later changed the administrate language of the Ghaznavid state from Arabic to Persian.