The observed microwave brightness temperature of soils depends upon the soil temperature profile, which in a remote sensing application will not be known in any detail. In this paper we discuss a parameterization of effective soil temperature, which when divided into the brightness temperature gives the emissivity, in terms of surace (T0) and deep (T∞ ) soil temperatures as T = T∞+ C(T0-T∞). A coherent radiative transfer model and a large data base of observed soil moisture and temperature profiles are used to calculate the best fit value of the parameter C. For 2.8, 6.0, 11.0, 21.0, and 49.0 cm wavelengths the C values are respectively, 0.802¿0.006, 0.667¿0.008, 0.480¿0.010, 0.246¿0.009, 0.084¿0.005. The parameterized equation gives results that are generaly within 1 or 2% of the exact values.