The well-known method for the determination of mercury(IT), which is based on the anodic stripping voltammetry of mercury(II), has been adapted for applications at the thin film poly(3-bexylthiophene) polymer electrode. Halide ions have been found to increase the sensitivity of the mercury response and shift it more positive potentials. This behavior is explained by formation of mercuric halide which can be easily deposited and stripped from the polymer electrode surface. The procedure was optimized for mercury determination. For 120 s accumulation time, detection limit of 5 ng mL(-1) mercury(II) has been observed. The relative standard deviation is 1.3% at 40 ng mL(-1) mercury(II). The performance of the polymer film studied in this work was evaluated in the presence of surfactants and some potential interfering metal ions such as cadmium, lead, copper and nickel.