A simple cyclic voltammetry (CV) analytical method with organo-modified sericite for the working electrode was investigated to detect As(III) in an aquatic environment, and optimal conditions for the reliable measurement of trace amounts of As(III) were studied. A distinct, specific peak was clearly observed at 0.8 V due to the reduction of H3AsO4 to H3AsO3. The specific peak current of arsenic increased with increasing the concentration of As(III) and initially increased proportionally to the scan rates. However, it disappeared as the scan rate increased over 400 mV/s. Because the surface of the organo-modified sericite electrode rapidly became saturated with As(III) when the deposition time increased, an optimal deposition time was determined as 60 s. Pb(2+) had no significant influence on the peak signal of As(III), whereas it was reduced as the ratio of Cu/As increased. Considering the detection limit of arsenic (1 ppb), this system can be used to detect low levels of As(III) in water systems.