A low cost and easy-to-construct electrochemical sensor is fabricated for the determination of arsenite in water by using an Fe(dmbpy)32+-exchanged (dmbpy=4,4′-dimethyl-2,2′-bipyridine) Nafion (Nf) film. Arsenite at a glassy carbon electrode (GCE) coated with the Fe(dmbpy)32+-exchanged Nf film is shown to be electrocatalytically oxidized at lower overpotentials than at a bare GCE, and a tentative mechanism is proposed for the electrocatalytic oxidation. This new electrochemical sensing platform (ESP) exhibits a wide linear calibration range (from 10 μM to 100 mM) with a correlation coefficient above 0.99 for the precise determination of arsenite; the ESP exhibits a detection limit of 10.0 μM for arsenite determination. Utility of the developed sensor is further assured by determining the concentration of arsenite present in standard aqueous samples and in samples from different water sources. Among the several interferences studied, high concentrations of Zn2+ (50 times higher than arsenite) can affect arsenite determination. Kinetic parameters, such as the diffusion coefficient, catalytic rate constant, and so forth, are determined by using chronocoulometry and chronoamperometry techniques.