A nonylphenol-degrading bacterial strain (YT(T)) was isolated previously from a river sediment sample obtained in Ami-machi, Ibaraki, Japan, and identified as a Sphingomonas species. In this study, the taxonomic relationship between strain YT(T), a recently described nonylphenol-degrading strain, Sphingomonas cloacae, and Sphingobium yanoikuyae, which is phylogenetically related, was examined. Their phenotypic characteristics were compared and levels of DNA-DNA relatedness between these strains were determined. Based on the results of physiological and biochemical tests and DNA-DNA hybridization, it is proposed that strain YT(T) (=IAM 15006(T)=JCM 11777(T)=CIP 107839(T)) represents a novel species of the genus Sphingobium, Sphingobium amiense sp. nov.