Cyclic voltammogram of methiocarb in 0.1 M H2SO4 exhibited an irreversible anodic peak at about +1285 mV versus Ag/AgCl. Electro-oxidation and determination of methiocarb in spiked soil, river water and agrochemical formulation were realized on a newly prepared carbon-nanotube paste electrode by applying square wave voltammetry (SWV). The dE (p) /dpH value indicated that the oxidation mechanism involved the coupling of H+ with the oxidation process. The peak signals were linearly related to methiocarb concentration in the range of 1.5-59.1 mgL(-1) with a detection limit of 0.45 mgL(-1). The accuracy and selectivity of the proposed method were shown by calculating the recoveries of methiocarb from soil, river water and pesticide formulation Mesurol(A (R)). The calculated percent recoveries for soil and river water samples spiked with 30.0 mu g g(-1) and 40.0 mu g mL(-1) levels were 99.3 +/- A 1.2 and 98.5 +/- A 0.3 at 95 % confidence limit, respectively.