A Gram-positive, spore-forming, rod-shaped bacterium, designated J1^T was isolated from deep-sea mud collected from the South China Sea and subjected to polyphasic taxonomic investigation. Phylogenetic analysis based on 16S rRNA gene sequences revealed that J1^T clustered with the type strains of Amphibacillus cookii , Amphibacillus sediminis and Amphibacillus jilinensis and exhibited a range of similarity of 93.9–97.0 % to members of the genus Amphibacillus . The DNA G+C content was 36.7 mol%. Chemotaxonomic analysis showed no quinones, and the cell wall contained meso-diaminopimelic acid as the diagnostic diamino acid for strain J1^T. The major cellular fatty acids were iso-C_{15 : 0} and anteiso-C_{15 : 0}. Strain J1^T was positive for catalase activity and negative for oxidase activity. On the basis of phylogenetic position and phenotypic properties, strain J1^T represents a novel species of the genus Amphibacillus and the name Amphibacillus marinus sp. nov. is proposed. The type strain is J1^T ( = CGMCC 1.10434^T = JCM 17099^T).