When zeta potential is measured by the method of electrophoretic light scattering, the frequency shift of scattered light is typically no more than a few hundreds of hertz. If the power spectrum of the scattered light is calculated in the full-band, the frequency resolution will be reduced. To improve the frequency resolution, the full-band power spectrum is estimated first through the discrete Fourier transform, then the refined spectrum is analyzed in a narrow-band by a linear frequency modulating chirp Z-transform, and finally the frequency shift of the scattered light is obtained with good resolution. We have designed an instrument based on laser Doppler electrophoresis and have used it to measure the zeta potential of three types of polystyrene latex standard particles. The experimental data show that the chirp Z-transform improves the precision of zeta potential measurement and gives a measurement repeatability better than 5%.