A bacterial strain, isolated from a sample of reef-building coral (Isopora palifera) collected off the coast of southern Taiwan, was characterized using a polyphasic taxonomic approach. The strain, designated sw-2(T), was Gram-staining-negative, aerobic, rod-shaped and motile, with subpolar flagella, and formed greyish pink colonies. Phylogenetic analyses based on 16S rRNA gene sequences indicated that strain sw-2(T) was most closely related to Roseivivax halodurans Och 239(T) (97.4 % sequence similarity) and Roseivivax halotolerans Och 210(T) (96.4 %). The novel strain did not require NaCl for growth and exhibited optimal growth at 35-40 �XC, at pH 7.5-8.0 and with 3-7 % (w/v) NaCl. It produced bacteriochlorophyll a under aerobic conditions. Summed feature 8 (C(18:1)�s7c and/or C(18:1)�s6c; 63.7 %) predominated in the cellular fatty acid profile. The novel strain's major respiratory quinone was ubiquinone Q-10 and its genomic DNA G+C content was 68.8 mol%. The polar lipid profile consisted of a mixture of phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, diphosphatidylglycerol, phosphatidyldimethylethanolamine, sulfo-quinovosyl diacylglycerol and three uncharacterized phospholipids. The level of DNA-DNA relatedness between strain sw-2(T) and Roseivivax halodurans Och 239(T) was only 15.0 %. The results of physiological and biochemical tests allowed the clear phenotypic differentiation of the novel strain from all established species of the genus Roseivivax. Based on the genotypic, phenotypic and chemotaxonomic data, strain sw-2(T) represents a novel species in the genus Roseivivax, for which the name Roseivivax isoporae sp. nov. is proposed. The type strain is sw-2(T) (= LMG 25204(T) = BCRC 17966(T)).