A swing control system for a hybrid construction machine has a swing operating lever, an electric swing motor, a speed detection sensor which detects the rotary speed of a swing motor, a controller that calculates the driving speed of the swing motor by a swing operating signal created by the operation of the swing operating lever and by a detecting signal of the rotary speed, an inverter which drives the swing motor by a control signal from the controller, a swing inertia detector that detects the swing inertia of equipment and an inertia torque compensator which compares the torque compensation value in accordance with the equipment inertia, and outputs a calculated torque value for controlling the swing motor to the inverter.