Immunochemical assay, ELISA for small molecules such as pesticides are rapid, sensitive, cost effective and can easily analyze with large samples. ELISA is one of several powerful biotechnologies immediately applicable to pesticide analysis. This review lists the advantages and disadvantages of the ELISA and elucidate the steps in assay development using examples from this laboratory. The focus is primarily on hapten synthesis strategies, protein conjugation, Immunization, assay format, and assay validation.