In recent decades, organophosphorus (OP) pesticides are widely used in agricultural and domestic fields. There is increasing demand for more rapid and economical methods of detecting pesticide residues. We have developed a gold immunochromatography assay (GICA) strip test for detecting a group of OP pesticides based on monoclonal antibodies (MAb) against a generic hapten, O,O-diethyl O-(4-carboxy-3-methylphenyl) phosphorothioate. The MAb showed desirable properties for use in indirect competitive ELISA, and the minimum IC50 value (93 ng/mL) was observed in chlorpyrifos-ethyl curve. The partially purified monoclonal antibodies were conjugated with colloidal gold particles. The conjugation of the colloidal gold and antibodies was monitored by ultraviolet-visible (UV-vis) spectroscopy and fluorescence spectroscopy, while the transmission electron microscopy (TEM) images were used to characterize the particle size and shape of the conjugates. Dynamic light scattering (DLC) was applied as a less expensive and faster method to substitute TEM. The colloidal gold and antibody conjugates were used for the production of a GICA strip test to detect OP pesticides. Preliminary assessment suggests that the OP pesticide, chlorpyrifos-ethyl (CE), in environmental samples could be detected by the GICA strip. This assay could potentially be used for screening large volume of samples and on-spot monitoring before the precise analysis. But the homogeneity of the detection needs to be improved further.