A thermophilic, alkaliphilic and catalase-positive bacterium, designated strain HA6(T), was isolated from a hot spring in China. The strain was aerobic and chemo-organotrophic and grew optimally at 60 degrees C, pH 8.5 and 1.5 % (w/v) NaCl. The cells were Gram-positive rods, forming single terminal endospores. The predominant cellular fatty acids were iso-C(15 : 0) and iso-C(17 : 0). The cell-wall peptidoglycan contained meso-diaminopimelic acid. The genomic DNA G+C content was 45.2 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that strain HA6(T) formed a distinct lineage within the family Bacillaceae and was most closely related to Bacillus horti K13(T) and Bacillus smithii DSM 4216(T), with sequence similarities of 91.8 and 93.1 %, respectively. On the basis of its physiological and molecular properties, strain HA6(T) should be placed in a novel genus and species, for which the name Caldalkalibacillus thermarum gen. nov., sp. nov. is proposed. The type strain of Caldalkalibacillus thermarum is strain HA6(T) (=CGMCC 1.4242(T)=JCM 13486(T)).