A bicycle derailer includes abuse member, a movable member and a linkage assembly. The base member is mounted to a bicycle frame. The movable member moves between a retracted position and an extended position at which the movable member is farther from the base member than the retracted position. The linkage assembly operatively couples the base member and the movable member. The linkage assembly includes a first link, a second link, an extension link and a sliding link. The first and second links are pivotally coupled between the base member and the movable member. The extension link extends from one of the first and second links toward the other of the first and second links. The sliding link includes a sliding portion slidably coupled to the extension link to slide along the extension link and a pivoting portion pivotally coupled to the other of the first and second links.