A Gram-stain-negative, non-motile, aerobic and rod-shaped bacterial strain, designated H-12T, was isolated from a sea squirt (Ciona savignyi) collected from Tsingtao Port, Jiaozhou Bay, China, and its taxonomic position was investigated. Strain H-12T grew optimally at 25-30 °C, at pH 7.0-8.0 and in the presence of 3.0-4.0 % (w/v) NaCl. The 16S rRNA gene sequence of strain H-12T exhibited the highest similarity to that of the type strain of Amylibacter marinus (95.3 %). A neighbour-joining phylogenetic tree based on 16S rRNA gene sequences revealed that strain H-12T clustered with the type strain of A. marinus. The predominant ubiquinone in strain H-12T was identified as Q-10. The major fatty acids of strain H-12T were C18 : 1ω7c and C18 : 1ω7c 11-methyl. The major polar lipids detected in strain H-12T were phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, one unidentified aminolipid, two unidentified phospholipids and five unidentified lipids. The DNA G+C content of strain H-12T was 52.7 mol%. On the basis of phylogenetic, chemotaxonomic and phenotypic properties, strain H-12T is considered to represent a novel species within the genus Amylibacter, for which the name Amylibacter cionae sp. nov. is proposed. The type strain is H-12T (=KCTC 52581T=CGMCC 1.15880T).