MLO proteins are highly conserved proteins with seven trans-membrane domains. Specific MLO genes have been linked to plant disease susceptibility. Others are involved in plant reproduction and in root thigmomorphogenesis. Functions of the remaining MLOs are still unknown. Here we performed a genome-wide survey of the MLO family in eight legume species from different clades of the Papillionoideae sub-family. A total of 118 MLO sequences were identified and characterized. Their deduced protein sequences shared the characteristics of MLO proteins. The total number of MLO genes per legume species varied from 13 to 20 depending on the species. Legume MLOs were evenly distributed over their genomes and tended to localize within syntenic blocks conserved across legume genomes. Phylogenetic analysis indicated that these sequences clustered in seven well-defined clades. Comparison of MLO protein sequences revealed 34 clade-specific motifs in the variable regions of the proteins. Comparative analyses of the MLO family between legume species also uncovered several evolutionary differences between the tropical legume species from the Phaseoloid clades and the other legume species. Altogether, this study provides interesting new features on the evolution of the MLO family. It also provides valuable clues to identify additional MLO genes from non-sequenced species.