Abstract: The present invention offers the monoclonal antibodies that have a high specificity to ciguatoxins, which are the causative poisons of the ciguatera poisoning. The monoclonal antibodies were produced using synthetic hapten conjugates as artificial antigens, which were prepared by the conjugation of a synthesized hapten consisting of the IJKLM-ring fragment of ciguatoxins with proteins such as KLH, BSA, etc. The monoclonal antibodies show a specific reactivity to ciguatoxins, but little or almost no reactivity to other marine polyether toxins such as the okadaic acid, etc.