The essential non-uniform distribution of particle mass concentration, with vivid maximum value inside the two-phase laminar boundary layer developed in the how past a flat plate, has been found by experimental investigation. The mathematical model based on the approximation of the dispersed phase within the viscous fluid, taking into consideration pseudoviscosity coefficients, has been elaborated for description of the motion and distribution of solid admixture. The dispersed phase is considered as a polydispersed phase, which consists of a finite number of particle fractions. The numerical results from the simplest version of the model are in good agreement with the experimental results, which indicates a principal possibility of applying the given mathematical model for flows of similar type.