A Cu(II)-rutin complex was prepared with a metal to ligand molar ratio of 3:2 by mixing stoichiometric amounts of rutin and CuCl2. The isolated complex was characterized by IR and UV/Vis spectroscopy and incorporated into a plasticized PVC-membrane using o-nitrophenyloctylether as a plasticizer (66% plasticizer, 33% PVC and 1% Cu(II)-rutin complex). The sensing characteristics of the membrane against Cu(II) ion were investigated using direct potentiometry. The membrane showed -4 a Nernstian response for Cu(II) ion with a slope of 28.5 mV/decade of activity between 5 x 10and 4-2 x 10M. The influence of several inorganic cations on the response of the Cu(II)-rutin complex based membrane was also investigated and the corresponding potentiometric selectivity coefficients were estimated and optimized with Solver (Excel).