The deposition of aluminium oxide 12 and 23 μm particles onto a horizontal flat plate within the laminar boundary layer in the free-stream moderate turbulent flow was studied. The present numerical model considered the deposition onto the surface to be a probabilistic process determined both by hydrodynamics and the adhesive behaviour of particles and surface. Numerical simulation was realised for the flat-plate laminar boundary layer. The two-fluid approach was used for writing the Euler equations for a carrier gas and particulate phase. The effects of gravity and lift forces on the particles velocities and mass concentration, occurring within the boundary layer, and deposition were studied separately for various particle sizes. It was revealed that gravity and lift forces have decisive influence on the behaviour of solid particles taken place within the laminar boundary layer and on their deposition that is expressed via the distributions of the particles transverse velocity and mass concentration. These effects become more pronounced for the larger 23 μm particles. This fact, coupled with the higher probability of entrainment by the surface, results in their larger deposition velocity. The given study is the attempt to combine the hydrodynamic and adhesive aspects of the particles deposition for its more accurate estimate that is suitable for various practical devices.