A novel sulfate-reducing bacterium, strain S606T, was isolated from a sulfide sample collected at a depth of 2764 m from a deep-sea vent chimney wall in the Indian Ocean. Phylogenetic 16S rRNA gene sequence analyses placed strain S606T within the genus Thermodesulfatator , with highest sequence similarity of 98.2 % to Thermodesulfatator indicus DSM 15286T, followed by Thermodesulfatator atlanticus AT1325T (97.4 %). The average nucleotide identity (ANI) values between S606T and the two other type strains (T. indicus DSM 15286T and T. atlanticus AT1325T) were 79.2 % and 71.5 %, respectively. The digital DNA–DNA hybridization estimate values between S606T and these two type strains were 22.7±2.4 % and 18.1±2.3 %, respectively. Cells were Gram-stain-negative, anaerobic, motile rods (1–1.8×0.5–0.7 µm). The novel isolate grew at NaCl concentrations ranging from 1.5 to 4.5 % (optimum 2.5–3 %), from pH 5.5 to 8 (optimum 6.5–7.0) and at temperatures between 50 and 80 °C (optimum 65–70 °C). S606T grew chemolithoautotrophically in an H2/CO2 atmosphere (80 : 20, v/v; 200 kPa), used sulfate as a terminal electron acceptor, but not sulfur, sulfite nor thiosulfate. The predominant fatty acids were C16 : 0 (24.2 %), summed feature 8 (C18 : 1ω6c and/or C18 : 1 ω7c, 26.3 %), C18 : 0 (22.2 %) and C18 : 1ω9c (9.2 %). The DNA G+C content of the chromosomal DNA was 43.1 mol%. The combined genotypic, chemotaxonomic and phenotypic traits show that S606T should be described as representing a novel species of the genus Thermodesulfatator , for which the name Thermodesulfatator autotrophicus sp. nov. is proposed. The type strain is S606T (=DSM 101864T=MCCC 1A01871T).