A bicycle rear derailleur includes a seat assembly, a movable component, a linkage assembly, and a chain guide. The seat assembly includes a first seat body, a second seat body, and a shaft. The shaft is disposed through the first seat body and the second seat body and configured to be mounted on the bicycle frame, and the second seat body is configured to connect the first seat body with the bicycle frame. The linkage assembly connects the movable component with the first seat body. The chain guide is pivotably disposed on the movable component. The first seat body is movable towards or away from the second seat body along a central line of the shaft.