A strain of free-living obligately anaerobic, halophilic spirochaete, SLT, was isolated from a sample of a cyanobacterial mat of the hypersaline Solar Lake, Sinai shore. The strain had motile helical cells, 0.35-0.40 × 6-10 μm. Strain SLT exhibited high resistance to NaCl among known halophilic spirochaetes growing at NaCl concentrations from 2 to 12% (optimum growth at 7%). The strain grew at temperatures from 10 to 32 °C (optimum at 28 °C) and pH from 6 to 8.5 (optimum at pH 7.0-7.5). Carbohydrates, but not alcohols, organic acids or nitrogenous compounds (peptone, yeast extract and amino acids), were used as energy substrates for growth. Ethanol, acetate, lactate, H2 and CO2 were the products of glucose fermentation. Sulfide was produced in the presence of S0 or thiosulfate in the medium. The DNA G+C content was 44.7 mol%. Based on 16S rRNA gene sequence analysis, strain SLT clustered within the genus Spirochaeta, exhibiting 94.2 and 93.7% similarity with its closest relatives, Spirochaeta bajacaliforniensis DSM 160554T and Spirochaeta smaragdinae DSM 11293T, respectively; similarity with other species did not exceed 86%. The phenotypic and chemotaxonomic characteristics of the strain, as well as the results of phylogenetic analysis support the classification of strain SLT as representing a novel species of the genus Spirochaeta, for which the name Spirochaeta sinaica sp. nov. is proposed. The type strain is SLT ( = DSM 14994 = NIQEM U 783).