Surface complexation of phthalic acid/phthalate has been investigated on synthetically produced, nonaged gamma-aluminum oxide by infrared and Raman spectroscopy. Effects of time, pH, and ionic strength have been studied both on the total adsorbed amount of phthalate and on the surface complexes. The spectroscopic results indicated the formation of two different types of complexes: outer sphere and inner sphere. The relative concentrations of these complexes were shown to vary considerably with pH but very little with increasing ionic strength, which equally reduced the amount of both types of complexes. Considering the electrostatic interaction between the surface and adsorbate, a complexation model was proposed that is in accordance with the spectroscopic results. Adsorption on the synthetic gamma-alumina was compared to the adsorption on gamma-aluminum oxide films produced by anodic oxidation, where the adsorbed amount was greatly reduced; however, both inner- and outer-sphere types of complexation have been observed.