A novel Gram-stain-negative, catalase- and oxidase-positive, motile, short rod-shaped bacterium designated BGMRC 6574T was isolated from stems of Aegiceras corniculatum collected from Hainan province, China. The strain grew at 25-37 °C (optimal at 28 °C), pH 5.0-10.0 (pH 7.0), and 3-8% (w/v) NaCl (3%). Based on the 16S rRNA phylogenetic analysis, the strain was closely related to Pararhizobium haloflavum MCCC 1K03228T (96.45% sequence similarity). The novel strain showed an average nucleotide identity value and a digital DNA-DNA hybridization of 72.62 and 27.1%, respectively, to P. haloflavum MCCC 1K03228T based on draft genome sequences. The G+C content of the genomic DNA was 64.7 mol%. The major respiratory quinone was Q-10. The strain possessed genes putatively encoding choline uptake and conversion to betaine gene clusters. The extract significantly delayed the lifespan of Caenorhabditis elegans compared to the control (P < 0.05). The major polar lipids were phosphatidylcholine, seven unidentified phospholipids, three unidentified ninhydrin-positive phospholipids, and two unidentified lipids. The major cellular fatty acid was C19:0 cyclo ω8c. The results of a polyphasic taxonomic study showed that strain BGMRC 6574T represents a new species of the genus Pararhizobium, and it was named Pararhizobium mangrovi sp. nov. The type strain is BGMRC 6574T (=KCTC 72636T = CGMCC 1.16783).