The microwave transmission technique was applied to simultaneously monitor the moisture and salt contents in a butter-making process. The dielectric properties of a salted water-in-oil (W/O) emulsion as a model of salted butter was investigated. The dielectric loss tangent, tan delta, of a non-salted W/O emulsion was independent of the volume fraction of the dispersed phase, whereas that of the salted W/O emulsion increased with increasing volume fraction of the dispersed phase below a frequency of 3 GHz. It was theoretically confirmed that the moisture and salt contents of the salted W/O emulsion could be evaluated from the linear formula for phase shift and attenuation in the same frequency region, and that the electrolyte had more effect on attenuation than the phase shift. The moisture and salt contents of salted butter could be simultaneously monitored in the butter-making process by means of a linear regression formula for the phase shift and attenuation at a frequency of 3 GHz in a concentration range between 15.5 and 17.5% by weight, and between 1.0 and 2.0% by weight, respectively.