The temperature influence on the output signal of a closed-loop fiber-optic gyroscope (FOG) is discussed. An appropriate technique has been developed and used to study the influence of temperature changes on individual FOG components such as integrated optics circuit, superluminescent fiber light source, and fiber optic coil. Certain components have been found to impact most strongly on the output signal. A thermal mathematical model of the FOG has been developed. A qualitative agreement between the experimental data and the calculations is reported. The ways of minimizing the thermal impact on the output signal are proposed