A short-rod-shaped, Gram-negative, motile bacterial strain, designated CS-6(T), was isolated from a water sample collected from a spring located inside Nature Valley, Hsinchu County, Taiwan, and was characterized using a polyphasic approach. Phylogenetic analyses based on 16S rRNA gene sequences showed that the strain formed a monophyletic branch at the periphery of the evolutionary radiation occupied by the genus Aquabacterium in the class Betaproteobacteria. The closest neighbours were Aquabacterium parvum B6(T) (96.7 % sequence similarity), Aquabacterium commune B8(T) (96.6 %) and Aquabacterium citratiphilum B4(T) (95.9 %). The predominant fatty acids were 18 : 1omega7c (30.5 %), 16 : 0 (27.9 %) and summed feature 3 (16 : 1omega7c and/or iso-15 : 0 2-OH) (22.7 %). The DNA-DNA relatedness of the strain with respect to recognized species of the genus Aquabacterium was less than 70 %. The isolate was also distinguishable from members of the genus Aquabacterium on the basis of phenotypic and biochemical characteristics. It is evident from the genotypic, chemotaxonomic and phenotypic data, therefore, that strain CS-6(T) represents a novel species of the genus Aquabacterium, for which the name Aquabacterium fontiphilum sp. nov. is proposed. The type strain is CS-6(T) (=LMG 24215(T)=BCRC 17729(T)).