A mathematical model was developed to monitor the facilitated transport of germanium(IV) from oxalic acid solutions through a flat sheet supported liquid membrane (FSSLM) containing Cyanex 923. This model presented a reliable calculation of the extraction constant (K ex = 2.057 × 10 3 1/mol 4 ). The FSSLM model was solved according to the extraction reaction, Fick's law, and diffusional transport. Consequently, the overall mass transfer coefficient (K org ) was found to be 3.84 cm/s. Using this value, diffusion coefficients for various Cyanex 923 concentrations in the range of 5 to 30 %v/v were calculated. Finally, the accuracy of the models was investigated.