Air conditioning system including a temperature sensor for sensing a room temperature, an MET (metabolic) sensor for sensing an activity amount of people in a room, a dust sensor for sensing a dust amount, a gas sensor for sensing an intensity of smell, a VOC (Volatile Organic Compounds) sensor for sensing a compound amount, a fan driving unit for controlling an air flow rate, a heater for raising a room temperature, an anion generating unit for generating anion, and a control unit for controlling the fan driving unit and the heater according to an operation condition preset with reference to a sensed room temperature and the activity amount of people in the room, and controlling the fan driving unit and the anion generating unit according to an operation condition preset with reference to a sensed dust amount, the intensity of smell, and the VOC amount, thereby enhancing comfortability, and performing effective cleaning function, and displaying room cleanliness in real time on a screen, to improve a product reliability.