A Gram-negative, strictly aerobic, motile bacterium with flagella, designated strain G210(T), was isolated from a crude-oil-contaminated tidal flat of the Taean coast in South Korea. Cells were non-spore-forming, ovoid rods showing catalase- and oxidase-positive reactions. Growth of strain G210(T) was observed between 15 and 45 °C (optimum, 30-35 °C) and between pH 5.5 and 9.0 (optimum, pH 6.5-7.5). Strain G210(T) contained Q-10 as the sole isoprenoid quinone and summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and C19 : 0 cyclo ω8c as the major fatty acids. Putrescine and spermidine were identified as the major polyamines. Strain G210(T) contained phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, phosphatidylmonomethylethanolamine, an unidentified phospholipid and an unidentified aminolipid as polar lipids. The G+C content of the genomic DNA was 56.9 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain G210(T) formed a phyletic lineage with members of the genus Aquamicrobium. Strain G210(T) was most closely related to Aquamicrobium ahrensii 905/1(T) (97.9 % similarity). The DNA-DNA relatedness between strain G210(T) and the type strain of A. ahrensii was 24±0.5 %. On the basis of phenotypic, chemotaxonomic and molecular properties, strain G210(T) represents a novel species within the genus Aquamicrobium, for which the name Aquamicrobium aestuarii sp. nov. is proposed. The type strain is G210(T) ( = KACC 14931(T) = JCM 16876(T)).