In this paper the permeation process of trace cobalt(II) through supported liquid membranes using di(2-ethylhexyl)phosphoric acid as a mobile carrier was modeled and the rate-controlling mechanism was examined. The permeation rate equations were derived considering diffusion of metal ions across the aqueous stagnant layers toward the membrane, chemical reaction at the feed-membrane interface, and diffusion of extractant and its metal complex in the membrane phase. The application of the measured permeation rates for determining the kinetic parameters of the solvent extraction reaction was also investigated. It was found that the calculated rates were in good agreement with the measured ones (average standard error, 12%).