The distribution of neodymium(III) between acidic aqueous nitrate solutions and organic solutions of di(2-ethyl-hexyl)phosphoric acid (D2EHPA) in hexane has been studied for different extractant and metal ratios at constant aqueous ionic strength 0.1 M (Na+,H+-NO3). The distribution data have been evaluated by both graphical and numerical analysis, in order to determine the speciation in the organic phase. The results obtained suggest the formation of two complexes in the organic phase: NdA3-3HA, which is predominant when the extractant/metal ratio is higher than one, and NdA3, which is the main species when the ratio is equal to one. For lower concentrations of extractant it has been found that the possible formation of species at the interface creates difficulties in the modelling of the extraction process.