Fifteen strains of red-pigmented, strictly aerobic, coccoid, extremely halophilic archaea were isolated from fish sauce (nam-pla) produced in Thailand. They grew optimally at 37 degrees C, pH 6-8 and in the presence of 20-30 % (w/v) NaCl. The DNA G+C contents of the isolates were 60.0-61.8 mol%. They had MK-8(H2) as a major menaquinone component and C(20)C(20) and C(20)C(25) derivatives of phosphatidylglycerol, phosphatidylglycerol methylphosphate and a sulfated glycolipid, S-DGA-1, as major polar lipid components. 16S rRNA gene sequence comparisons revealed that a representative strain, HDB5-2(T), was affiliated with Halococcus dombrowskii JCM 12289(T), Halococcus qingdaonensis JCM 13587(T) and Halococcus morrhuae JCM 8876(T) (levels of similarity of 98.2-98.7 %). Based on data from DNA-DNA hybridization experiments, the 15 strains represented a single species, showing hybridization values of >78.9 % to representative strain HDB5-2(T), but were unrelated to either Halococcus dombrowskii JCM 12289(T) or Halococcus morrhuae JCM 8876(T), with levels of relatedness of <50 %. Moreover, a comparison of phenotypic properties discriminated these new isolates from recognized species of the genus Halococcus. The 15 strains are thus considered to represent a novel species of the genus Halococcus, for which the name Halococcus thailandensis sp. nov. is proposed. The type strain is HDB5-2(T) (=BCC 20213(T) =JCM 13552(T) =PCU 278(T)).