The process of microfiltration in the dead-end mode when the flow of a polydispere suspension that has the log-normal density distribution of particle diameters is perpendicular to the membrane working surface has been considered. The probabilistic sieving mechanism developed earlier by the authors is used to describe the process of filtration through a heterogeneous membrane that has a bilog-normal diameter distribution density of pores. The integral equation for determining the productivity of the membrane in time is solved numerically for five different positions of the maximum of the diameter distribution density of particles relative to two maximums of the size distribution density of membrane pores. The results are illustrated by plots to reflect time changes in productivity and rejection factor of the membrane and in pore size distribution during pore blocking.