The extraction of Ce (III) from aqueous solutions containing Al (NO3)(3) was examined by using styrene-divinylbenzene copolymer (SDB) gels swollen with dihexyl-N,N-diethylcarbamoylmethylphosphonate (CMP), octyl(phenyl)-N,N-diisobutylcarbanoylmethylphosphine oxide (CMPO) and an equimolar mixture of CMP and CMPO. The extraction constants (K-ex) for the gels with CMP and CMPO were evaluated. The distribution ratio of Ce(III) for the gel with an equimolar mixture of CMP and CMPO was described as K-d=(K-ex(CMP)[CMP](3) + K-ex(CMPO) [CMPO](3))[NO3-](3)) by using these extraction constants, The extraction rate was found to be controlled by diffusion of ce-complex [Ce(NO3)(3) (CMPO)(3) or Ce(NO3)(3) (CMP)(3)] through the gel. The diffusion coefficient (Ds) was inversely proportional to the viscosity of extractant (eta) and represented by an expression Similar to the Stokes-Einstein equation, D-s eta/T = constant. A decrease in the viscosity of extractant was effective for increasing the extraction rate.