Extraction of o-aminophenol (OAP) using trialkylphosphine oxide (TRPO) was studied with different diluents. The neutral OAP was extracted using TRPO under an equilibrium pH in the range of 6-7.5, and a maximum distribution coefficient occurred. It was confirmed that the pH value and the TRPO concentration are the key factors that affect distribution coefficient. Nonpolar diluents could provide better extraction distribution coefficient for the extraction of OAP and the order is: kerosene >n-octanol >chloroform.