Line M8, officially referred to as the M8 Bostancı-Parseller line, is a rapid transit line of the Istanbul Metro. The line connects Bostancı railway station, on the southern coast of the Anatolian side, to Parseller, in the district of Ümraniye. At Bostancı, connections are available with intercity trains to destinations in Anatolia, as well as the Marmaray service across the Bosphorus.

The line is 14.27-kilometre (8.87 mi) long with 13 stations. It opened for service on 6 January 2023.

It is a fully automatic driverless metro line; all stations have platform screen doors and are completely underground.