A neutrophilic, stalk-forming, iron-oxidizing bacterium, strain OYT1(T), which was isolated from a groundwater seep in Ohyato Park, Tokyo, Japan, was subjected to taxonomic analysis. OYT1(T) was a motile, bean-shaped, Gram-negative bacterium that was able to grow at 8-30 °C (optimally at 25-30 °C) and at pH 5.6-7.3 (optimally at pH 6.1-6.5). The strain grew microaerobically and autotrophically. Major cellular fatty acids detected were C16 : 1ω7c/C16 : 1ω6c and C16 : 0. The total DNA G+C content was 57.6 mol%. 16S rRNA gene sequence analysis revealed that strain OYT1(T) was affiliated with the class Betaproteobacteria and clustered with iron-oxidizing bacteria isolated from groundwater seeps and wetlands and with uncultured clones detected in freshwater iron-rich environments. Based on the phenotypic and phylogenetic characteristics of strain OYT1(T), we propose that the strain represents a novel species in a new genus, for which the name Ferriphaselus amnicola gen. nov., sp. nov. is proposed; the type strain of Ferriphaselus amnicola is OYT1(T) ( = JCM 18545(T) = DSM 26810(T)).