D.300 is a major east–west state road spanning 2,004 km (1,245 mi) through central Turkey.

[1] The route begins in Çeşme, İzmir and runs east to Kapıköy, Van, on the Turkey-Iran border.

The route connects several provincial capitals, including İzmir, Uşak, Afyon, Konya, Aksaray, Kayseri, Malatya, Elazığ, Muş and Van.

The route is the second longest state highway in Turkey, after the D.400.

The D.300 is a four-lane highway for most of the route, except for two short sections toward the western end.