İslahiye is a municipality and district of Gaziantep Province, Turkey. Its area is 865 km², and its population is 67,650 (2022). It is a railway border crossing into Syria. Near İslahiye is the site of ancient Nicopolis.

The railway station of Islahiye is the last stop on the railway to Damascus in Syria. Since March 2001, a regular train line runs once a week between Syria and Iran via Islahiye. The state road D.825, which connects Gaziantep with Antakya, runs through İslahiye.

The town is inhabited by Yörüks of the Aydınlı tribe. English traveler Mark Sykes recorded İslahiye as a town inhabited by Turks in early 20th century.

A magnitude 7.8 earthquake struck İslahiye on 6 February 2023, causing widespread devastation in the town and many deaths.

There are 71 neighbourhoods in İslahiye District:

İslahiye has a hot-summer Mediterranean climate (Köppen: Csa), with very hot, dry summers, and cool, wet winters.