Ventilating system for introducing outdoor air and discharging room air, and method for controlling the same, the ventilating system including a duct for making a room and an outside of the room in communication, a ventilator connected to the duct for discharging room air to an outside of the room, and supplying outdoor air to the room through the duct, a window controller provided to each window for opening/closing the window individually, and a controller for controlling the ventilator and the window controller for ventilating the room. The method for controlling a ventilating system includes the steps of measuring conditions of room air and outdoor air, determining a ventilating method and a ventilating rate according to the measured conditions, and ventilating the room by opening/closing the window automatically, and putting a ventilator into operation according to a result of determination.