The fungicide diethofencarb has been studied by square wave voltammetry (SWV) using a multi wall carbon nanotube paste electrode (MWCNTPE). The peak potentials have been shifted in a more negative direction with increasing pH, showing a maximum peak response at +861 mV (vs. Ag/AgCl) and pH 2.0. Operational parameters affecting the sensitivity and selectivity such as accumulation potential (E-acc), accumulation time (t(acc)), frequency (f) and pulse amplitude have been optimized. The constructed calibration curve was linear within a concentration range of 2.50 mu g mL(-1) to 30.5 mu g mL(-1). The calculated limit of detection (LOD) and limit of quantification (LOQ) values were 0.77 mu g mL(-1) and 2.57 mu g mL(-1), respectively. The determination was realized in the presence of various fungicides to demonstrate the selectivity, accuracy and applicability of the recommended method. Spiked tomato juice samples with 2.50-7.50 mu g mL(-1) diethofencarb were subjected to the proposed method and recoveries of over 97% and relative standard deviations of less than 3.8% reflected a high degree of accuracy and precision.