Aims: To investigate the effects of the salt concentration, incubation temperature and initial pH of the medium on the fermentative ability of the halophilic lactic acid bacteria, Tetragenococcus muriaticus and T. halophilus. Method and Results: The growth, lactic acid production and pH reduction ability of five strains of T. muriaticus and T. halophilus in MRS broth medium under various culture conditions such as salt concentration (3, 7, 15 and 23% NaCl), temperature (20, 30 and 40degreesC), and initial medium pH (5.8, 6.5 and 7.5) were investigated. Those of T. halophilus were seriously affected by a high salinity (23% NaCl); in contrast, those of T. muriaticus were affected by a low initial pH (5.8). Conclusions: The results indicate that high saline concentrations and low pH values have significant impact on the growth, lactic acid production and pH reduction ability of T. halophilus and T. muriaticus, respectively. Significance and Impact of the Study: This study appears to be important in biopreservation during the manufacture of fermented food products. Both T. muriaticus and T. halophilus may support each other in reducing pH in hypersaline or low pH environment. To our knowledge, this is the first report on the fermentation ability of T. muriaticus.