This work studies the mechanism of active transport of silver(I) through an immobilized liquid membrane (ILM) containing thiourea derivatives having sulfur as donor atoms, namely (N-(N＇,N＇-diethyl thiocarbamoyl)N "-phenylbenzamidine (TCBA) and 1,6-diethylcarbamoyl imino)-1,6-diphenyl-2,5 dithiahexane (TCTH) dissolved in cumene as mobile carrier. An uphill transport model has been described and equations have been derived taking into account aqueous boundary layer diffusion and liquid membrane diffusion as simultaneous controlling factors. In the present model, various separate cases were discussed using carrier TCBA and TCTH considering the possibility of each chemical species and evaluating diffusional membrane resistance for lower and higher concentration of extractants. The diffusion coefficients were observed to decrease with increase in the extractant concentration ranging from 1.0 x 10(-7) to 3.5 x 10(-6) mol cm(-3). Plotting [Ag](0)-[Ag](t) vs, time resulted in a slope of [L-0]A/Delta(o)V taking into account both complexing species, AgL and AgNO3L, in the membrane. The validity of this model was evaluated with experimental data and found to be well in agreement with theoretical values. The mass transfer coefficient (Delta(a)(-1)), the diffusion coefficient of the metal carrier species (D-o) and the thickness of the aqueous boundary layer were calculated from the proposed model for TCBA and TCTH. The mathematical equation was derived to correlate the permeability flux with support characteristics such as porosity, tortuosity and thickness.