In this paper, the competitive permeation of cobalt and nickel from nitrate solutions through supported liquid membranes was studied, in which contained 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEHEHP) dissolved in kerosene as a mobile carrier. The permeation rate equations were derived taking into account the aqueous film diffusion of metal ions towards and out of the membrane and the membrane diffusion of HEHEHP and its metal complexes. The mass transfer coefficients of metal ions and metal-HEHEHP complexes were also determined using the permeation cell. It was found that the calculated permeation rates were in good agreement with the measured ones.