Fourier transformed infrared spectrometry (FTIR) and 27Al Magic Angle spinning (MAS) nuclear mag-netic resonance spectroscopy were employed to characterize arsenate adsorption on amorphous AI gels with Keggin structure at pH=4-10. These studies have proven that: the surface complex species of arsenate show significant dif-ferences under acidic and alkaline conditions, which was deduced based on the As-O stretching vibration bands lo-cated respectively at 774 and 870 cm-1; poorly crystalline Al13 (or Al)-arsenate precipitation could be easily formed under acid medium condition and high loading level, which was supported by comparing the As-O vibration (at≈732 cm-1) of precipitation to adsorbed Al gels; arsenate (AsO43-) adsorption has no effect on the Keggin structure of Al gels with basicity (R) =2.6 and 3.0, even at high loading level, as evidenced by the signal at ≈63×10-6 of magic angle spinning (MAS)-27Al NMR. The adsorption envelope was determined by conventional batch experiments.