Two haloalkaliphilic archaeal strains, X21T and C112T, were isolated from soda lakes in Inner Mongolia Autonomous Region, China. Their morphology, physiology, biochemical features, polar lipid composition and 16S rRNA genes were characterized in order to elucidate their taxonomy. According to these data, strains X21T and C112T belong to the genus Natrialba, although there are clear differences with respect to their physiology and polar lipid composition between the two strains and the type species, Natrialba asiatica. On the basis of low DNA-DNA hybridizations, these two strains should be considered as new species of genus Natrialba. The names Natrialba hulunbeirensis sp. nov. (type strain X21T = AS 1.1986T = JCM 10989T) and Natrialba chahannaoensis sp. nov. (type strain C112T = AS 1.1977T = JCM 10990T) are proposed.