Transport of copper ions through a plasticized cellulose triacetate membrane containing lauric acid as carrier and tris(2-ethylhexyl)phosphate (TEHP) as plasticizer has been investigated. A comparative study of transport mechanism across such a membrane and a supported liquid membrane (SLM) containing the same carrier in THEP has been made. In both cases, transport mechanisms were controlled by the diffusion of 1:2 metal/carrier complex in the membrane and of copper ions through the aqueous diffusion layer at the source/membrane interface. Diffusion coefficient in the cellulose triacetate membrane, after normalization, was found to be 22 times lower than in the corresponding SLM.