The present invention relates to a modular power assisting system. In particular the present invention relates to a modular electric power assisting system that is adaptable to a vehicle/engine driven system so as to be operated/powered by electric system and/or its original power system. The synergistic combination of the motor system; motor control system and energy storage device coupled to the regenerative braking system of the present invention enables the power assisting system of the present invention to adapt to the vehicle/engine without involving substantial modifications in engine, power train, drive train and vehicle. The engine and electric motor exploits advantages of each of the power source based on the operating conditions of the vehicle/engine driven system by selectively responding to the engine's power demands so as to enhance fuel efficiency, reduce undesirable emissions and provide better drivability.