The 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, at which both competing phenomena compensate each other. The equilibrium water content, θ_eq, is correlated with the soil specific surface area. Based on knowledge of θ_eq, a temperature‐correction formula is presented that adjusts the TDR soil‐moisture measurements at various temperatures to the corresponding value at 25°C. This decreases the absolute measurement error of soil moisture, θ_TDR, by the factor of 2 as compared to the uncorrected values.