A Gram-negative bacterium, designated AD8(T), was isolated from a tidal flat of the Taean coast in South Korea. Cells were strictly aerobic, motile, ovoid rods or rods, with two lateral flagella on one side. Strain AD8(T) was catalase- and oxidase-positive and able to oxidize thiosulfate and reduce nitrate to nitrite. Growth of strain AD8(T) was observed at 15-40 °C (optimum 25-30 °C), at pH 5.0-9.5 (optimum pH 6.0-7.5) and with 1.0-11.0 % (w/v) NaCl (optimum 2.0-4.0 %). The predominant fatty acids were C(18 : 1)ω7c and C(19 : 0) cyclo ω8c. The G+C content of the genomic DNA was 67.5 mol% and the major quinone was Q-10. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain AD8(T) belonged to the genus Citreicella and was most closely related to Citreicella marina CK-I3-6(T) within the class Alphaproteobacteria (96.9 % 16S rRNA gene sequence similarity). On the basis of phenotypic, chemotaxonomic and phylogenetic analysis, strain AD8(T) represents a novel species within the genus Citreicella, for which the name Citreicella aestuarii sp. nov. is proposed. The type strain is AD8(T) ( = KACC 13699(T) = DSM 22011(T)).