The main aim of this study is to treat palm oil mill effluent (POME) containing phenol, which is a hazardous compound, using activated carbon (AC) prepared from palm kernel shell (PKS), one of the byproducts of the palm oil industry. First, PKS from Thailand was characterized by proximate, elemental, and thermogravimetric analyses. The high carbon and low ash contents in the PKS indicated that PKS is a promising precursor for producing AC. Then, palm kernel shell activated carbon (PKSAC) was prepared using chemical activation with orthophosphoric acid as an activating reagent under various conditions. The physical and chemical properties of the PKSACs were characterized using nitrogen adsorption-desorption and Fourier-transform infrared spectroscopy (FT-IR), respectively. Chemical activation improved the yield and physical properties, even as it changed the chemical properties of PKSACs. The PKSACs thus prepared contained large volumes of micropores. Using the prepared PKSACs, batch equilibrium adsorption was conducted to remove phenol from the POME model. The PKSACs could successfully adsorb and remove phenol from the POME model. The phenol adsorption followed the Langmuir model, and the saturated adsorbed amount of phenol increased with increase in surface area. Based on these results, it is concluded that the treatment of POME using PKSACs produced by chemical activation would be a practicable treatment method since the prepared PKSACs provide a high yield and are capable of treating model hazardous compound in POME.