Based on the analysis of coupling location, coupling regent, carrying protein and coupling process, completed antigen of Microcystin-LR (MC-LR) was synthesized. A free amidogen was introduced to microcystin-LR (MC-LR) using chemical modification (aminoethylation) of its 7th core amino acids, N-methyl-dehydroalanine. The intermediate product Aminoethyl-MC-LR (H2N-etMC-LR) was purified by Solid Phase Elute (SPE) and identified by Mass Spectrometry, then coupled with BSA through glutaraldehyde to be complete antigen. The completed antigen was dialyzed and identified by SDS-PAGE, UV-scanning and bio-mass spectrometry. The result show that the coupling ratio between MC-LR and BSA of complete antigen in average was over 5, and it is sufficient to immunity.