2,4,5-Trichlorophenoxy acetic acid (2,4,5-T) is used in forestry and in agriculture as a systemic herbicide (for eradication of undergrowth, etc). Adsorption behaviour of 2,4,5-T on the surface of poly-o-toluidine Zr(IV) phosphate was studied and some thermodynamic parameters such as Freundlich constants and Langmuir constants were determined on the surface of cation-exchanger. In this work, the adsorption of 2,4,5-T on cation-exchanger from aqueous medium was studied with respect to pH and initial 2,4,5-T concentration. The experimental data were analyzed by the Freundlich isotherm, and the Langmuir isotherm. The results indicated that the cation-exchanger is very effective for the adsorption of 2,4,5-T from aqueous solutions. Pesticide sensitive membrane electrode was fabricated by using an electro-active composite material poly-o-toluidine Zr(IV) phosphate. The sensitivity towards the 2,4,5-T was monitored. (C) 2011 Elsevier B.V. All rights reserved.