A swing control system for a hybrid construction machine comprising: a swing manipulation lever that outputs a swing manipulation signal that is proportional to a manipulation amount by an operator; an electric swing motor that is driven in response to an electric control signal corresponding to the manipulation amount of the swing manipulation lever to cause an upper swing structure (b) to be swiveled with respect to a lower traveling structure (a); a speed detection sensor that detects a rotational speed of the swing motor; a controller that calculates a driving speed of the swing motor based on the swing manipulation signal by the manipulation of the swing manipulation lever and a rotational speed detection signal, which is fed back thereto from the speed detection sensor; an inverter configured to drive the swing motor based on a current value for control, which is applied thereto from the controller; a swing inertia detector configured to detect a swing inertia of the machine, which varies depending on a change in position of a work apparatus (c) and output a torque compensation value or a swing inertia detection signal corresponding to the torque compensation value according to the detected swing inertia of the machine; and an inertia torque compensator configured to compare the torque compensation value according to the machine inertia that is output from the swing inertia detector with a torque value output from the controller, and to output a calculated torque value for controlling the swing motor to the inverter, characterized in that the swing inertia detector detects a position change value of each of hydraulic cylinders for the work apparatus in real time and detects the swing inertia of the machine using a combination of the detected position change values of the hydraulic cylinders. a swing manipulation lever that outputs a swing manipulation signal that is proportional to a manipulation amount by an operator; an electric swing motor that is driven in response to an electric control signal corresponding to the manipulation amount of the swing manipulation lever to cause an upper swing structure (b) to be swiveled with respect to a lower traveling structure (a); a speed detection sensor that detects a rotational speed of the swing motor; a controller that calculates a driving speed of the swing motor based on the swing manipulation signal by the manipulation of the swing manipulation lever and a rotational speed detection signal, which is fed back thereto from the speed detection sensor; an inverter configured to drive the swing motor based on a current value for control, which is applied thereto from the controller; a swing inertia detector configured to detect a swing inertia of the machine, which varies depending on a change in position of a work apparatus (c) and output a torque compensation value or a swing inertia detection signal corresponding to the torque compensation value according to the detected swing inertia of the machine; and an inertia torque compensator configured to compare the torque compensation value according to the machine inertia that is output from the swing inertia detector with a torque value output from the controller, and to output a calculated torque value for controlling the swing motor to the inverter, characterized in that the swing inertia detector detects a position change value of each of hydraulic cylinders for the work apparatus in real time and detects the swing inertia of the machine using a combination of the detected position change values of the hydraulic cylinders.