The results of the scattering matrix measurements at a wavelength of 0.63 μm are presented for an aqueous suspension of lead oxide containing plate-like particles and their aggregates with monomers dimensions of ~ 5 nm. The results of the measurements are compared with the matrix calculations for axially symmetric scatterers (ellipsoids of revolution). It is shown that the presence of aggregates affects the scattering properties of such a medium. The particles size distribution of the dispersed medium was found by solving the problem of minimizing the sum of the squares of the deviations of the experimental values of the matrix elements from calculated using the model of axially symmetric scatterers. It is demonstrated that the particle size distribution is more accurately retrieved by minimizing the sum of the squares of the deviations for the sum of the diagonal elements. The obtained distribution is compared with one measured by the dynamic light scattering method. Keywords: scattering matrix, aggregates, particle size distribution, axially symmetric scatterers, dynamic light scattering