Immunoassay based on antigen-antibody interaction plays an important role in the screening of low molecular mass organic contaminations such as pesticides, veterinary drugs and biological toxins. However, due to the lack of epitope groups of haptens, the production of antibodies with high affinity is still one of the bottlenecks of immunoassay for small molecules. Dendrimers, as a new type polymer, exhibit many excellent structural properties and histocompatibility, such as clear molecular composition, regular, highly branched and nanometer-sized structure, monodisperse property and presenting dense functional groups on its surface. Previous studies had revealed that dendrimers are potential in the improving performance of immunoassay, such as to produce antibodies with higher affinity, produce antibodies with broad-specificity and improve assay sensitivity. In this work, therefore, the application of dendrimers as carrier to prepare immunogens and coating antigens, as adjuvant to improve immunogenicity, as carrier to amplify signal were reviewed. The potential of application of dendrimers on the development of immunoassays for small molecules was also discussed.