Langevin dynamics (LD) was used to simulate Brownian diffusion of aerosol particles with absorption walls on both sides. The results of LD calculations were compared with analytical solutions of the diffusion equation. Differences between the results obtained by LD calculation and the diffusion equation were organized by the dimensionless number Kn' which was proposed to be the ratio of the path length of a Brownian particle lambda(P) to the distance between two walls L. When Kn' > 10(-4), results of LD calculation differed significantly from the analytical solution of the diffusion equation. When Kn' > 10(-2), the concentration of aerosol particles calculated by LD exceeded the analytical solution of the diffusion equation by 5% in relative error.