Rhizobia are Gram-negative bacteria known for their ability to fix atmospheric N2in symbiosis with leguminous plants. Current evidence shows that rhizobia carry in most cases a variable number of plasmids, containing genes necessary for symbiosis or free-living, a common feature being the presence of several plasmid replicons within the same strain. For many years, we have been studying the mobilization properties of pSmeLPU88b from the strainSinorhizobium melilotiLPU88, an isolate from Argentina. To advance in the characterization of pSmeLPU88b plasmid, the full sequence was obtained. pSmeLPU88b is 35.9 kb in size, had an average GC % of 58.6 and 31 CDS. Two replication modules were identifiedin silico: one belonging to therepABCtype, and the other to therepC. The replication modules presented high DNA identity to the replication modules from plasmid pMBA9a present in anS.melilotiisolate from Canada. In addition, three CDS presenting identity with recombinases and with toxin-antitoxin systems were found downstream of therepABCsystem. It is noteworthy that these CDS present the same genetic structure in pSmeLPU88b and in other rhizobial plasmids. Moreover, in all cases they are found downstream of therepABCoperon. By cloning each replication system in suicide plasmids, we demonstrated that each of them can support plasmid replication in the S.melilotigenetic background, but with different stability behavior. Interestingly, while incompatibility analysis of the clonedrepsystems results in the loss of the parental module, both obtained plasmids can coexist together.