Organophosphorous pesticide(OP) contamination has serious adverse effects on human health and the environment. Due to the toxicity of OPs and the threat presented by their accidental or intentional release in populated areas, the determination and monitoring of these OPs in food products and environment is of great importance. OPs are present in very small quantities and therefore, methods for their detection need to be highly sensitive and selective. Here, we aimed to develop a simple and selective aptamer-based colorimetric assay for the detection of omethoate, which is one of the commonly used OPs. The principle of the assay is that single-stranded DNA(ss DNA)-wrapped gold nanoparticles(Au NPs) are resistant to salt-induced aggregation. By employing an “artificial antibody” organophosphorous pesticide-binding aptamer(OBA) as the recognition element, aptamer-wrapped Au NPs(Au-apta) show high selectivity towards omethoate, resulting in the disconnection of aptamers from Au NPs and the aggregation of Au NPs. As there is a significant color change from the interparticle plasmon coupling during the aggregation of Au NPs, the established assay showed good linearity between 0.1 and 10 μmol/L, with a low detection limit of 0.1 μmol/L. Other OPs such as profenofos, phorate, and isocarbophos would not interfere with the detection of omethoate despite having similar structures. Thus, the colorimetric method shows potential for use in the detection of omethoate in real soil samples. Due to the toxicity of OPs and the threat presented by their accidental or intentional release in populated areas, the determination and monitoring of OPs in food products and environment is of great importance. OPs are present in very small quantities and therefore, methods for their detection need to be highly sensitive and selective. Here, we aimed to develop a simple and selective aptamer-based colorimetric assay for the detection of omethoate, which is one of the commonly used OPs. The principle of the assay is that single-stranded DNA (ss DNA) -rapped gold nanoparticles (Au NPs) are resistant to salt-induced aggregation. By employing an “artificial antibody ” organophosphorous pesticide-binding aptamer (OBA) as the recognition element, aptamer-wrapped Au NPs (Au-apta) show high selectivity towards omethoate, resulting in the disconnection of aptamers from Au NPs and t he aggregation of Au NPs. As there is a significant color change from the interparticle plasmon coupling during the aggregation of Au NPs, the established assay showed good linearity between 0.1 and 10 μmol / L with a low detection limit of 0.1 μmol / L. Other OPs such as profenofos, phorate, and isocarbophos would not interfere with the detection of omethoate in having similar structures. Thus, the colorimetric method shows potential for use in the detection of omethoate in real soil samples.