An experiment was designed and conducted under the stable-controllable conditions in order to minimize the uncertain influences from in situ measurements in the estuarine water. Sediment particles from the Yangtze River estuary and the Yellow River estuary as two typically turbid estuaries in China were sampled in the field, screened and resampled in the laboratory. Furthermore, the quantitative relationships of backscattering coefficient and suspended sediment particle size, and of backscattering coefficient and remote-sensing reflectance were theoretically analysed. The effects of the particle size of sediment on remote-sensing reflectance were experimentally observed. The results provide the basis for the modelling of case-2 waters and the parameterized expression of particle size in the model in future work.