The influence of soil moisture in thermal infrared emissivity is a known fact, but poorly studied in the past. An experiment for quantifying the dependence of emissivity on soil moisture has been designed. Six samples of superficial horizons of different Mediterranean soil types have been selected. Their emissivity has been measured at different soil water contents, using the two-lid variant of the box method, whereas the gravimetric method has been selected for obtaining the soil moisture. As a result, the study shows that emissivity increases significantly when water content becomes higher, especially in sandy soils in the 8.2-9.2 μm range. A set of equations has been derived to obtain emissivity from soil moisture at different spectral bands for the analysed soil types.