A control system for a vehicular drive unit having an engine, a motor-generator for acting as a motor and a generator; a power transmission including a planetary gear composed of at least three rotary elements and a mechanism for selectively connecting/releasing the rotary elements; a battery for storing electric power generated by the motor-generator and for supplying a driving electric power; a residue detector for detecting the state of charge of the battery; and a controller for controlling the engine, the motor-generator and the connecting/releasing mechanism in accordance with an output signal from the residue detector. The first rotary element of the planetary gear is connected to the output shaft of the engine; the second rotary element, as acting a reaction against the first rotary element, is connected to the motor-generator; and the third rotary element is connected to an output member for transmitting the drive power to wheels. The controller includes mode switching capability for switching the mode when the battery is in an ordinary state or in a low charge state, to a power split mode, in which the motor-generator outputs a reaction torque against the output torque of the engine so that the connecting/releasing mechanism can rotate the first, second and third rotary elements individually and, when the battery is in a full charge state, to a parallel hybrid mode, in which the motor-generator adds a torque to the output torque of the engine so that the connecting/releasing mechanism can rotate the first and second rotary elements together.