Although the autoinducers of Mesorhizobium loti could not be detected under the conditions of experimentally pure culture, and even adding some root exact of Lotus japonicus into the medium in which M. loti grew to detect the acyl-homoserine lactone (AHL) production, no positive result has been available. However, analysis of homologous comparison showed that there were at least four annotated acylated homoserine lactone (AHL) synthase genes from M. loti genome sequences. The amino acids of all these four genes showed different homologous to those of lux I , tra I and lax I all of which were AHL synthase genes and have been studied most before. By cloned into the expression vector of pET30a and transformed into Escherichia coli BL21, one of these synthase genes, m14543 was overexpressed in E. coli, and a strong 20kDa protein band could be got by SDS-PAGE of the recombinant cells. It has been detected that at least three different AHLs were produced in the recombinant strain with IPTG induced. These results indicated that M. loti has the quorum sensing system and it may work under some specific growth conditions, most likely involved in the microbe-plant interaction. This study means to give some clues to any further study of the quorum sensing system of M. loti .