Zeta potential of protein particles was an essential indicator to evaluate soymilk stability, and before the measurement, dilution of soymilk was regarded as a necessary procedure. In order to guarantee the accuracy and scientificity of analysis results of zeta potential, appropriate diluent should be chosen. In this study, deionized water and soymilk permeate were respectively used to dilute soymilk, and the effects of these two diluents on zeta potential, size distribution, pH value and electrical conductivity of soymilk were compared. According to the results, if soymilk was diluted by deionized water, a remarkable increase in the absolute value of zeta potential could be observed with the increase of dilution ratio (*P<0.05), and it was mainly attributed to the dissociation of soymilk aggregations and the decrease of ionic strength, since the size of protein particles became smaller, the pH value deviated from that of soymilk, and the electrical conductivity was significantly decreased after the dilution (*P<0.05). By contrast, when soymilk permeate was the diluent of soymilk, the absolute value of zeta potential, as well as the size distribution of protein particles, the pH value and the electrical conductivity, did not change with the increase of dilution ratio, which indicated that the charged stability of soymilk protein particles was well kept after the dilution. Therefore, soymilk permeate could be considered as an ideal diluent in the measurement of zeta potential.%蛋白粒子zeta电位是衡量豆乳体系稳定性的一个重要指标，而在电位分析前常采用稀释介质对豆乳进行预处理。为了确保zeta电位测定的准确性和科学性，必须选择合适的稀释介质。因此，该研究采用去离子水、豆乳超滤液两种稀释介质分别对豆乳进行稀释，并比较了这2种稀释介质对zeta电位、粒径分布、pH值以及电导率的影响。结果表明，若以去离子水为稀释介质，zeta电位的绝对值会随着稀释倍数的升高而显著增加（*P<0.05），这主要是由于豆乳蛋白胶体粒子发生解聚导致粒径减小，而pH值的升高和电导率的降低则说明豆乳的离子强度显著降低。相比之下，选用豆乳超滤液稀释豆乳时，体系的 zeta 电位、粒径分布、pH值以及电导率都未随稀释倍数的增加而改变（*P>0.05），说明此法能够较好地维持豆乳蛋白粒子的荷电稳定性。由此可知，豆乳超滤液可做为豆乳zeta电位测定的理想稀释介质。
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