Carbon paste electrode (CPE) was modified with F-300 commercial activated carbon or Norit SX- 2 powdered activated carbon. CPEs were prepared for detection of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,6-dichlorophenoxyacetic acid (2,6-D) and 2,4,6-trichlorophenoxyacetic acid (2,4,6-T). The electrochemical behavior of these materials was investigated employing cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The modifier was found to enhance the electroactive surface area and the peak current in comparison to the bare (unmodified) carbon paste electrode. The intensity of the signal increased with the increase in adsorption ability of the modifiers. Compared to the unmodified electrode, all the new paste electrodes showed a much greater sensitivity for detection of chlorinated phenoxyacetic acids in water samples.