Di(2-ethylhexyl)phosphoric acid was used as a reagent for the extraction of o-aminophenol in 2-octanol and kerosene. Equilibrium data for active and inactive diluents were obtained at various di(2-ethylhexyl)phosphoric acid concentrations. Both neutral and positive forms of o-aminophenol could be extracted by di(2-ethylhexyl)phosphoric acid. The maximum distribution coefficient occurred when the initial pH value was between pK(a1) and pK(a2), the dissociation constants of o-aminophenol. At the same concentration the extractabilitiy of di(2-ethylhexyl)phosphoric acid increased as the polarity of the diluent increased. The difference of the distribution coefficient between polar diluents and nonpolar diluents decreased with an increase in the di(2-ethylhexyl)phosphoric acid concentration. Fourier transform infrared spectroscopic analysis was used to show that the behavior is controlled by ion association and ion exchange reactions.