Three electrical elements (i.e., resistance, capacitance, and relaxation frequency) of electrical double layer (EDL) formed around particles have been extracted by a measuring-fitting combination for a novel noninvasive online measurement technique of particle size and concentration in a liquid-particle mixture. The measuring-fitting combination means measuring the impedances with electrical-impedance spectroscopy (EIS) method, and fitting the equivalent circuit with Levenberg-Marquardt method. The liquid-particle mixture in the impedance measurement is made of sodium chloride solution and stainless particles; the equivalent circuit is established corresponding to the contents in the liquid-particle mixture. As a result, the influence of the particle size and concentration on the electrical elements in the EDL which are the resistance, capacitance, and relaxation frequency in the EDL are clarified and discussed. This method is useful for determination of the particle size and concentration in liquid-particle mixture.