Cadmium is recently threatening not only the life of man but also nature and living environment. In addition, cadmium usage is generally decreasing because it is toxic. 3-Methyl-4- (4-hydroxybenzylidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-one (MDT) in 0.1 M supporting electrolyte was attached to glassy carbon electrode (GCE) by the phenol oxidation. The modified surface was investigated by several methods. The stability of the prepared surface was presented. The GCE with MDT was utilized for Col(11) ions analysis in water samples. The concentration range and the detection limit were 1.0x10(-9)-1.0x10(-8) M and 2.0x10(-10) M, respectively.