A bicycle derailleur comprises a base member, a movable member, and a chain guide. The chain guide comprises an inner guide plate, an outer guide plate, at least one pulley axle, and at least one pulley. The chain guide is configured to be movable between a plurality of shifting positions. The at least one pulley is configured to be movable between the inner guide plate and the outer guide plate within a maximum pulley movable amount in a pulley axial direction with respect to a rotational center axis of the at least one pulley. A single shifting distance is defined between adjacent shifting positions of the plurality of shifting positions. A ratio of the maximum pulley movable amount to the single shifting distance ranges from 0.21 to 0.35.