AbstractForest fires are a recurrent natural phenomenon in the Mediterranean basin. Fires can affect physical, chemical and biological soil properties. The effects on soil properties are closely controlled by fire severity, which is a consequence of temperatures reached and the length of residence of heat in the soil. In this study, the response of glomalin‐related soil protein (GRSP) − a glycoprotein produced by arbuscular mycorrhizal fungi − to heating temperature has been studied. Laboratory heating treatments were carried out at 180°C, 200°C, 250°C, 300°C, 400°C and 500°C in soil samples from eight different sites in SE Spain. The sites selected had mainly different soil characteristics. The results of heating on soil water repellency and soil organic carbon (SOC) were also included in the study. GRSP response to temperature was different between sites. Redundancy analyses divided sandy soils from the rest of soil types. Total content of aggregates, SOC and clay and sand content were the most significant properties explaining the response of GRSP to heating treatments. Results showed that GRSP was affected even at low temperature. SOC response to temperature was very similar between sites. Soil water repellency did not appear after heating in wettable soils and disappeared in water‐repellent ones at temperatures over 200°C. Our results indicate that GRSP could provide relevant information about fire severity. Copyright © 2015 John Wiley & Sons, Ltd.