The adulteration of melamine into food is banned but its misuse has been widely reported in milk products and animal feed. The development of a rapid screening immunoassay for monitoring this substance is an urgent requirement. In this research, a hapten of melamine was successfully synthesized by introducing six carbon chain length spacer arm via a reaction between 6-aminocaproic acid and 2-chloro-4,6-diamino-1,3,5-triazine(CAAT). The molecular structure of this hapten was indentified by H¹ nuclear magnetic resornance spectrometry. An immunogen was prepared by coupling this hapten to Keyhole limpet hemocyanin (KLH). An enzyme conjugated was prepared by coupling synthesizedhapten to Horse raddish peroxidase (HRP). A direct competive ELISA (cELISA) was developed to evaluate assay performance. The results showed that high titer polyclonal antibodies were obtained, and the performance of this cELISAkit  showed good specification: IC₅₀ of 230 ng mL^-1, a LOD of 8.3 ng mL^-1, and LOQ of 10ng mL^-1. Regarding selectivity performance, no obvious cross-reactivity to common compound was found. This data showed that this ELISA kit met the requirement of melamine maximum residues level (1000 ng mL-1 in milk products, 2500 ng mL in animal feed), and could be use in an immunoassay for the rapid and sensitive detection of this banned chemical.