A novel thiosulfate-oxidizing bacterium, designated strain LCS2(T), was isolated from a biofilm on sulfur particles used in an autotrophic denitrification process. The strain was found to comprise Gram-negative, non-motile, non-spore-forming rods that produced yellow-pigmented colonies on R2A agar. The strain contained Q-8 as the major ubiquinone and 17 : 1 iso omega 9c, 15 : 0 iso and 17 : 0 iso as the major fatty acids. The G+C content of the genomic DNA was 64.6 mol%. The 16S rRNA gene sequence of strain LCS2(T) was found to be most similar to that of Rhodanobacter fulvus IAM 15025(T) (97.4 % similarity). The results of DNA-DNA hybridization and phenotypic analysis showed that strain LCS2(T) can be distinguished from all known Rhodanobacter species and therefore represents a novel species of the genus, for which the name Rhodanobacter thiooxydans sp. nov. is proposed. The type strain is LCS2(T) (=DSM 18863(T) =KCTC 12771(T)).