Adsorption of p-Nitrophenol by three different activated carbons (F100, S.E.I. and B.D.H.) was carried out at 301 K and at controlled pH conditions. Two different adsorption models (Langmuir model and Freundlich model) were studied and compared. The adsorption capacity of the carbons depends on the Point of Zero Charge (PZC) and surface area of the carbons. Adsorption of the solute at higher pH was found to be dependent on the concentration of anionic form of the solutes. The isotherm data were fitted to the Langmuir and Freundlich isotherm equations to obtain the relative parameters.