The eddy diffusivity coefficient of particles depends on the flow characteristics and on the physical properties of the particles. Experimental data and theoretical considerations suggest that the ratio of the eddy diffusion coefficient of particles (D-TP) to the eddy diffusion coefficient of fluid (D-T) is dependent mainly on the friction velocity of fluid (U-*), the sedimentation velocity of the particles (V-s), the Reynolds number (Re) of the flow and also the relative roughness of channel.(epsilon/D). It is shown here that this relation among these parameters may be represented as D-TP/D-T = mu(R) proportional to (U-*(m)/V-S)(n), where m and n are empirical constants. Some new empirical relationships are proposed for the eddy diffusion coefficient of particles in the turbulent flow in vertical or horizontal channels. The results compare favorably with experimental data from the literature. (C) 2002 Elsevier Science Ltd. All rights reserved.