A competitive enzyme-linked immunosorbent assay (ELISA) was developed for the quantitative detection of organophosphorus insecticide cyanophos. An analogue (hapten) of cyanophos was synthesized and was coupled to BSA to produce polyclonal antibodi es from rabbits. The antisera were screened against another hapten coupled to ovalbumin (OVA). Using the sera of highest specificity, an antigen-coated ELISA was developed, which showed an I50 of 310 ng/mL with the detection limit of 20 ng/mL. The antibodies showed negligible cross-reactivities with other organophosphorus pesticides except for parathion-methyl, which makes the assay suitable for the selective detection of cyanophos.