Indonesia is ranked fifth country with the world's most preterm baby (675,700 babies). The Grashof incubator is one of the most important biomedical tools to maintain the survival of the premature baby by keeping the temperature in the baby's cabin at temperature 33°-35°C. This Grashof incubator utilizes the principle of natural convection and natural circulation. The main components are the lamps as the main heater and the digital thermostat as a temperature control that set at a certain temperature. In this research, the temperature measurement method is using DS 18B20 sensor to measure temperature and DHT22 sensor to measure relative humidity, both of these sensors will be integrated with arduino board and software for data reading. The temperature measurement procedure is based on Indonesian National Standard (SNI). The purpose of this research is to know the temperature stability point in baby's cabin and to know the characteristic of temperature change in incubator following ambient temperature. The data were collected at environmental temperature variations 25 °C -30 °C and <25 °C in some conditions, 2x25 watt and 2x40 watt heater lamp, and thermostat usage. The results of the tests mentioned that the temperature stability level in the baby cabin, are strongly dependent on the environmental temperature.