This paper presents a method for measuring the emissivity and temperature simultaneously by a spot infrared thermometer. Theoretically, it is possible to determine both the emissivity and temperature by providing the two ambient temperatures and measuring the corresponding outputs of the thermometer. To verify this, a simple experimental apparatus was fabricated having a hemisphere aluminum bowl to uniform the ambient temperature of the test surface. The ambient temperature was varied by the electric heating wire attached on the aluminum bowl. As a result, it was suggested that this measurement is possible if the emissivity was not less than about 0.5. Since various error factors were considered to exist in this measurement system, it is necessary to reduce the main factors to improve the measurement accuracy.