An aerobic, Gram-stain-negative, rod-shaped bacterial isolate, strain NH36A(T), was isolated from a sandy sediment sample from the South China Sea. Colonies of the isolate were dark orange on M2 agar. Optimal growth was observed at pH 7.0-8.5, 30 degrees C and in the presence of 0.5-4.0 % (w/v) NaCl. The major fatty acids were C(15 : 0), iso-C(15 : 0), anteiso-C(15 : 0), iso-C(15 : 1), iso-C(15 : 0) 3-OH, iso-C(17 : 0) 3-OH and summed feature 3 (comprising iso-C(15 : 0) 2-OH and/or C(16 : 1)omega7c). The DNA G+C content was 38.9 mol%. 16S rRNA gene sequence analysis revealed that strain NH36A(T) was most closely related to members of the genus Arenibacter, exhibiting 94.3-96.2 % sequence similarity to the type strains of Arenibacter species. On the basis of phenotypic, chemotaxonomic and phylogenetic data, this organism should be classified as a representative of a novel species in the genus Arenibacter. The name Arenibacter nanhaiticus sp. nov. is proposed and the type strain is NH36A(T) (=LMG 24842(T)=CCTCC AB 208315(T)=MCCC 1A04137(T)).