Twenty-nine rhizobial isolates from root nodules of Astragalus and Lespedeza spp. growing in the Loess Plateau of China were characterized by numerical taxonomy, RFLP and sequencing of PCR-amplified 16S rRNA genes, measurement of DNA G+C content, DNA–DNA relatedness and cross-nodulation with selected legume species. Based on the results of numerical taxonomy, the isolates formed two clusters (1 and 2) with some single isolates at a similarity level of 82 %. Cluster 1 contained six isolates from Astragalus and Lespedeza spp. Cluster 2 consisted of nine isolates from Astragalus spp. DNA relatedness was greater than 80% among isolates within cluster 2. Phylogenetic analysis based on 16S rRNA gene sequences showed that CCBAU 7190BT, representing cluster 2, was closely related to Rhizobium galegae and Rhizobium huautlense. DNA–DNA relatedness between CCBAU 7190BT and reference strains of R. galegae, R. huautlense and other related species ranged from 0 to 48?6 %. The cluster 2 isolates could also be differentiated phenotypically from related species. Based on these data, a novel species, Rhizobium loessense sp. nov., is proposed for cluster 2, with the type strain CCBAU 7190BT (=AS1.3401T=LMG 21975T).