IntroductionThe purpose of this study is to determine the temperature influence on the soil bulk dielectric permittivity, ε b , calculated from the measurement of the electromagnetic wave velocity of propagation along the parallel waveguide in a TDR probe, i.e. a probe working in Time Domain Reflectometry technique. The experimental evidence shows that the existing models do not completely describe the temperature effect. However, it has been confirmed that the observed temperature effect is the result of two competing phenomena; ε b increases with temperature following the release of bound water from soil solid particles and ε b decreases with temperature increase following the temperature effect of free water molecules. It has been found that there is a soil type characteristic moisture value, θ eq , named the equilibrium water content, having the specific temperature property. The temperature effect for this moisture is not present, which means that for soils with the moisture value equal to θ eq the both competing phenomena mentioned earlier compensate each other. The equilibrium water content, θ eq , decrease is correlated with the soil specific surface area. The temperature correction formula adjusting the soil moisture determined by TDR, θ TDR , at various temperatures to the corresponding value at 25°C, based on knowledge of θ eq , decreases the standard deviation of the absolute measurement error of soil moisture θ TDR by the factor of two as compared to the uncorrected values.