A bicycle rear derailleur guard assembly for use with a bicycle having a derailleur mounted to a frame of the bicycle by a derailleur mounting bolt. The derailleur guard assembly preferably includes a body supportable by an axle assembly of the bicycle. The body is configured to extend from an axis of the axle assembly to a space adjacent the mounting bolt of the derailleur and defines an inner surface facing the frame when the guard assembly is mounted to the bicycle. A support is configured to support the derailleur when the guard assembly is mounted to the bicycle and, in at least one arrangement, the body is positioned outwardly of the derailleur mounting bolt within the space adjacent the mounting bolt.