A mathematical model of mass transfer in the boundary layer of swirl flow is developed. The equations obtained for Sherwood number and mass transfer coefficient generalize the equations obtained by Levich for the flat plate to the case of mass transfer in axisymmetrical swirl flow. For the first time it is shown that, in swirl flows, the mass transfer is not completely controlled by integral flow parameters (Reynolds number and the swirl number) but depends essentially on the type of vortex symmetry. The left-handed helical vortices generate wake-like swirl flows and increase mass transfer in comparison with axial flows. The right-handed helical vortices generate jet-like swirl flows, which can decrease mass transfer.