Line U4 is a line on the Vienna U-Bahn metro system.

Opened in 1976, it currently has 20 stations and a total length of 16.5 km (10.3 mi), from Hütteldorf to Heiligenstadt.

[1] It is connected to U1 at Karlsplatz and Schwedenplatz, U2 at Schottenring, U3 at Landstraße, U6 at Längenfeldgasse and Spittelau.

Line U4 currently serves the following stations:[2]