It was previously demonstrated that ultrasound enhances mass transfer rates of solutes across various biological and artificial membranes. The mechanisms that govern these processes are still largely unknown. In this study, a classical convective dispersion approach was used to model the mass transfer of large molecules (proteins) through the small pore size membranes (15-50 nm) exposed to the ultrasound field. The model seems to satisfactorily describe the process occurring in the thin pores where diffusion of large molecules is hindered by the wall effects during exposure to low frequency ultrasound (20 kHz). The model offers a possible explanation of controlling the rate of diffusion enhancement by the intensity of ultrasound field.