A bicycle derailleur is provided with a chain guide that basically includes inner and outer guide plates, a guide pulley and a tension pulley. The tension pulley is rotatable about a rotation axis between free ends of the guide plates. The tension pulley has an annular recess disposed about the rotation axis to form a projection. The inner guide plate has a guide section with a radially outermost edge. Preferably, the outermost edge of the guide section is located in the annular recess, and the projection projects axially further from a center plane of the tension pulley than the outermost edge. Preferably, the chain guide includes a dust cap coupled between the inner guide plate and the tension pulley. Preferably, the outermost edge of the guide section is located radially inwardly of the projection and radially outwardly of the annular portion of the dust cap.