Abstract: A motorized window blind includes a mounting frame stretched in a longitudinal direction, a blind screen including a mounted end mounted on the mounting frame, a liftable end opposite to the mounted end in a transverse direction relative to the longitudinal direction, and a flexible intermediate portion interposed therebetween. A motor has an output shaft and is mounted in the vicinity of the mounting frame so as to drive a drive transmitting member to move a distal end of the drive transmitting member in the transverse direction between retracted and extended positions where the distal end is proximate and distal to the mounting frame, respectively. A plurality of tubes are telescopically fitted to each other, and extend in the transverse direction.