A simple competitive immunoassay was developed for the detection of fenthion in food samples. We employed the avian antibodies (IgY) that recognised fenthion as a capture reagent and fenthion-alkaline phosphatise conjugate as an enzyme label. The assay depended on the competitive binding between the antibody and fenthion extracted from spiked food samples for binding sites with immobilised fenthion-OVA conjugate. The concentration of fenthion in the food samples was quantified by the ability of the pesticide present in food samples to inhibit the binding of the enzyme conjugate to the antibody and subsequently the colour formation in the assay. The assay was specific to fenthion with a limit of detection of 100fg mL-1. Mean analytical recovery of fenthion in different food samples was 13–88%.The precision of the assay was satisfactory. The assay compared favourably with gas chromatography (GC) in its ability to accurately measure fenthion in the food samples.