A gas concentration measurement system and an airway adapter thereof are provided. The gas concentration measurement system includes the airway adapter and a gas concentration detection device including a main body. The main body includes an accommodating passageway, a check unit, a transmitter unit and a receiver unit. The airway adapter includes an inlet section, a detection section, an identification part and an outlet section. The detection section includes a light entering detection window and a light exiting detection window that are integrally formed. The identification part has an identification chip disposed therein. When the airway adapter is mated with the accommodating passageway of the gas concentration detection device along an axis of the airway adapter, the identification chip of the identification part is read to check whether or not the airway adapter is matched with the gas concentration detection device.