The diffusiophoretic velocities of carnauba wax and paraffin aerosol particles have been measured by injecting them as a thin sheet into a laminar flow of clean gas, with a water vapour concentration gradient established across it. In the range 0.1-1 of the Knudsen number, the measured velocities was found to increase with the diameter of aerosol particles. The experimental results were in better agreement with the Derjaguin and Yalamov theory (In G.M. Hidy, JR, Brock (Eds.), International reviews of aerosol physics and chemistry vol. 3 (Topics in current aerosol research, Part. 2). Pergamon Press, Oxford, 1972, p. 384.) than with those of Waldmann and Schmitt (In C.N. Davies (Ed.), Aerosol Science, Academic Press, London, 1966, pp. 137-162.), and Beresnev et at. (J. Aerosol Sci. 30 (Suppl. 1) (1999) S761).