The paper discusses the examination of the thermal expansibility of a coating composed of the austenitic steel 310S using the X-ray diffraction technique. Temperature measurements were made in the temperature interval of Tamb200°C, in which the transition of the metastable bcc phase forming the as-applied coating into an fcc-type phase occurred in the coating. The values of the coefficients of thermal expansion of both phases were determined by using the weighted average of the intensities of diffraction reflections recorded. The values of the coefficients of thermal expansion of both phases within the entire examination range (Tamb200°C), determined as the weighed averages with the weight allowing for the intensities of individual reflections, were found to be, respectively, 0.910-5 K-1 for the bcc phase and 1.510-5 K-1 for the fcc phase, and by approx. 0.110-5 K-1 lower than the values typical of the phases of austenite and ferrite in conventional steels.