In this paper, the amount of phenol in Meram, Karatay and Selcuklu regions in Konya tap water samples was quantified in aqueous medium by using 3,3'-diaminobenzidine (DAB) modified glassy carbon (GC) electrode. The electrode surface was modified with DAB in 0.1 M tetrabutylammonium tetrafluoroborate (TBATFB) using 100 mV s(-1) scanning rate between -0.5 V and + 1.5 V with 10 cycles. For the calibration curve, a series of standard phenol solution between 1.0 x 10(-12) M and 1.0 x 10(-3) M was prepared using pH 12. The prepared standard solutions were used for the chemical binding of phenol to the modified electrode surface between 0.0 V and + 1.1 V potential range using 100 mV s(-1) scanning rate with 10 cycles. By using this calibration method, the amount of phenol was determined as 1.23 x 10(-10) M, 3.03 x 10(-8) M and 1.99 x 10(-9) M in natural tap water samples in Britton-Robinson (BR) buffer solution at pH 12. Detection limit was obtained as low as 1.0 x 10(-10) M. The presence of DAB, phenol at the GC surface and phenol of DAB modified GC electrode surface was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.