Air pollution can be caused by natural sources and human activity. Now many say the polluted air around us. Carbon monoxide (CO) and carbon dioxide (CO2) is a parameter for determining the quality of clean air and polluted. If levels of these two substances excessive inhaled by humans, can be detrimental to health. By using the Arduino Mega 2560, air quality monitoring system in this study using LM35 sensor to determine the temperature of the air, MQ-7 sensor to determine the levels of CO and sensor MQ-135 to determine the levels of CO2 that is in the room. Sensor MQ-7 will be equipped with red and green LED indicator as the level of air quality is polluted or not polluted. If the levels of CO < 5 ppm, the green LED turns on and vice versa CO > 5 ppm, the red LED lights up. Likewise, CO2 levels <350 ppm, the green LED turns on and vice versa CO> 350 ppm, the red LED lights up. Research and simulation results show that the system works well. In the application of smart city, one of the important parameters is the monitoring system, in this research will be designed air quality monitoring system for the application of smart city.