Previous studies have demonstrated that bis-(3',5')-cyclic diguanosine monophosphate (bis-3',5'-c-di-GMP) is a ubiquitous second messenger employed by bacteria. Here, we report the identification of a bacterial intracellular signal, 2',3'-cyclic guanosine monophosphate (2',3'-cGMP), which controls the important biological functions, quorum sensing (QS) signaling systems and virulence in Ralstonia solanacearum through the receptor protein RSp0980. This signal specifically binds to RSp0980 with high affinity and thus abolishes the interaction between RSp0980 and the promoters of target genes. In-frame deletion of RSp0334, which contains a LLARLGGDQF region that catalyzes 2',3'-cGMP to (2',5')(3',5')-cyclic diguanosine monophosphate (2',3'-c-di-GMP), altered the abovementioned important phenotypes through increasing the intracellular 2',3'-cGMP levels. Furthermore, we found that the same 2',3'-cGMP signaling system exists in the human pathogen Salmonella typhimurium. As 2',3'-cGMP signal and homologs of both RSp0334 and RSp0980 are distributed in various bacterial species, our work might discover a widely conserved intracellular second messenger in bacteria.