A Gram-stain-positive, motile, rod-shaped bacterial strain, ISL-17T, was isolated from a marine solar saltern of the Yellow Sea, Korea, and its taxonomic position was investigated by means of a polyphasic study. Strain ISL-17T grew optimally at pH 8.5–9.0, at 37 °C and in the presence of approximately 10 % (w/v) NaCl. It contained meso-diaminopimelic acid as the diagnostic diamino acid in the peptidoglycan, MK-7 as the predominant menaquinone and iso-C15 : 0, anteiso-C15 : 0 and iso-C16 : 0 as the major fatty acids. The DNA G+C content was 48.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain ISL-17T fell within the genus Alkalibacillus, clustering with Alkalibacillus salilacus BH163T with a bootstrap resampling value of 100 %. Strain ISL-17T exhibited 98.2 % 16S rRNA gene sequence similarity to A. salilacus BH163T and 95.8–96.5 % similarity to the type strains of the other Alkalibacillus species. The mean DNA–DNA relatedness value between strain ISL-17T and A. salilacus KCTC 3916T was 19 %. The phenotypic properties of strain ISL-17T, together with its phylogenetic and genetic distinctiveness, enable this strain to be differentiated from recognized Alkalibacillus species. On the basis of phenotypic, phylogenetic and genetic data, strain ISL-17T represents a novel species within the genus Alkalibacillus, for which the name Alkalibacillus flavidus sp. nov. is proposed; the type strain is ISL-17T (=KCTC 13258T =CCUG 56753T).