RB 81 is the designation of several regional rail services in Germany:
, operated by DB Regio Bayern between Steinach (b Rothenburg o. d. Tauber) and Neustadt (Aisch) , operated by DB Regio Mitte between Trier and Koblenz , operated by DB Regio Nord between Bodenfelde and Nordhausen , operated by DB Regio Nord between Hamburg and Bad Oldesloe , operated by Erzgebirgsbahn between Chemnitz and Olbernhau-Grünthal , operated by VIAS between Darmstadt and Eberbach