A Gram-negative, non-spore-forming and rod-shaped, bacterium (designated Gsoil 531(T)) was isolated from soil of a ginseng field. On the basis of 16S rRNA gene sequence, strain Gsoil 531(T) clustered with species of the genus Mesorhizobium and was closely related to M. camelthorni CCNWXJ 40-4(T) (98.9%) and M. alhagi CCNWXJ12-2(T) (98.7%). The DNA G + C content was 62.9 mol% and the predominant quinone was ubiquinone-10 (Q-10). The major cellular fatty acids were C-16:0, C-19:0 cyclo omega 8c and summed feature 8 (C-18:1 omega 7c/C-18:1 omega 6c). The DNA-DNA hybridization values were less than 35.0% between novel isolate and its closest reference strains M. camelthorni HAMBI 3020(T), M. alhagi HAMBI 3019(T) and M tamadayense LMG 26736(T). Physiological, biochemical and low values of DNA-DNA hybridization results enabled strain Gsoil 531(T) to be differentiated genotypically and phenotypically from all known species of the genus Mesorhizobium. Therefore, strain Gsoil 531(T) signifies a novel species of the genus Mesorhizobium, for which the name Mesorhizobium hankyongi sp. nov. is proposed. The type strain Gsoil 531(T) (= KACC 19443(T) = LMG 30463(T)).