A new method of effective zeta-potential measurement by use of the liquid sedimentation balance method is developed. The test samples used were spherical silica particles, and an ultrasonic probe was used to enhance particle dispersion. In order to obtain reliable data, rapid change in sedimentation mass due to a small air bubble detachment from the detection tray is corrected in the data analysis process. The new method can be used to estimate the effective zeta-potential of each particle size range. The absolute value of negative zeta-potential of small particles is greater than that of large particles. The absolute values of negative zeta-potential increased with the increase of the ultrasonic probe power. The absolute value of negative zeta-potential shows a maximum value at the initial stage after the dispersion process, however it decreases over an elapsed time period. After an elapsed time greater than approximately 200 h, the zeta-potential shows a constant value. The data obtained by the new method qualitatively agreed with the conventional method. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.