Autoinducers from different strains of Mesorhizobium were detected with Strain KYC55(pJZ372) (pJZ384) (pJZ410). The results show that autoinducers widely exist in Mesorhizobium, and pH of the medium affects activities of the autoinducers seriously. Acidic condition is suitable for stability of the autoinducers. So red soil was chosen for extraction of autoinducers with ethyl acetate. It was found that the autoinducer activities varied with the ecological environments, sampling times and preservation conditions.