A rear sprocket assembly comprises a first sprocket and a lock device. The lock device includes a first lock member and a second lock member. The first lock member includes a first axial end and a second axial end. The second lock member includes a third axial end and a fourth axial end. The third axial end is configured to be attached to the second axial end of the first lock member in an assembled state where the first sprocket and the lock device are assembled as one unit. The fourth axial end has at least one radial projection configured to abut against a first sprocket in the axial direction in the mounting state. The lock device is configured so that the first sprocket is slidable relative to the lock device in the axial direction in the assembled state and before the mounting state.