The 1-octanol-water partition coefficients (logPow) of seven pesticides, i.e., Hymexazol, methomyl, imidacloprid, thiophanatemethyl, carbaryl, linuron, thiobencarb, were determined by RPHPLC method. The relation between these estimated logPow and adsorption isotherm parameters on powdered activated carbon was studied by correlating their logPow values with the Freundlich adsorption parameters. The adsorption parameter, logk, was found to increase with the increase of logPow for the pesticides examined. The activated carbon amount needed for lowering pesticide concentration from 500 μg/l to 50 μg/l was calculated. The amount of activated carbon needed for hymexazol (logPow, 0.11) was 688.5 mg/l, while that for thiobencarb (logPow, 3.78) was 5.1 mg/l, which suggests that pesticides with a high polarity, i.e., a low Pow, are difficult to remove by powdered activated carbon.