Gear unit and motor-driven gear unit for cable window lift system of motor vehicles, comprising drive and gear mechanism which cooperates with the drive and is coupled to rotatably mounted cable drum for winding/unwinding a cable of the system. Diameter of the cable drum of the gear unit ranges from about 22 mm to about 30 mm, preferably from about 24 mm to about 28 mm; gear ratio of the gear mechanism ranges from about 1:38 to about 1:55, preferably from about 1:42 to about 1:51. The cable drum has, on its end face, claws which engage in corresponding recesses on the end face of a worm wheel. Electric motors having maximum driving torque of only about 5.7 Nm can be used. The gear unit size can be reduced by about 40-50%, and it can be standardized for both electric and manual cable window lift systems for front or rear vehicle doors.