A curved, ring-like bacterium, strain AS 1.1761(T), isolated from the roots of Spartina anglica, was studied by a polyphasic approach. According to phylogenetic analysis, strain AS 1.1761(T) belongs to the genus Ancylobacter, with 99.21 % 16S rDNA sequence similarity to Ancylobacter aquaticus, the only species described so far in this genus. However, strain AS 1.1761(T) had no significant DNA-DNA binding with the type strain of A. aquaticus. In addition, strain AS 1.1761(T) differed from A. aquaticus in many phenotypic features. Based on molecular and phenotypic data, a novel species, Ancylobacter rudongensis sp. nov., is proposed. The type strain is AS 1.1761(T) (=JCM 11671(T)).