Common bean (Phaseolus vulgaris L.) can establish symbiotic associations with several Rhizobium species; however, the effectiveness of most strains at fixing nitrogen under field conditions is very low. PRF 81T is a very effective strain, usually referred to as Rhizobium tropici and used successfully in thousands of doses of commercial inoculants for the common bean crop in Brazil; it has shown high rates of nitrogen fixation in all areas representative of the crop in the country. Here, we present results that indicate that PRF 81T, although it belongs to the 'R. tropici group', which includes 10 Rhizobium species, R. tropici, R. leucaenae, R. lusitanum, R. multihospitium, R. miluonense, R. hainanense, R. calliandrae, R. mayense, R. jaguaris and R. rhizogenes, represents a novel species. Several morpho-physiological traits differentiated PRF 81T from related species. Differences were also confirmed in the analysis of rep-PCR (sharing less than 45% similarity with the other species), MLSA with recA, atpD and rpoB genes, and DNA-DNA hybridization. The novel species, for which we propose the name Rhizobium freirei sp. nov., is able to establish effective root nodule symbioses with Phaseolus vulgaris, Leucaena leucocephala, Leucaena esculenta, Crotalaria juncea and Macroptilium atropurpureum. The type strain is PRF 81T (5CNPSo 122T5SEMIA 4080T5IPR-Pv81T5WDCM 440T). © 2013 IUMS.