Strain AIS(T), an aerobic halophilic, Gram-reaction-negative, heterotrophic bacterium isolated from the water of Shira Lake in Khakasia, southern Siberia, was characterized using a polyphasic approach. Our analysis of the 16S rRNA gene sequences showed that 'Aliidiomarina haloalkalitolerans', 'Aliidiomarina sanyensis', Idiomarina maris and AIS(T) formed a distinct lineage. The sequence similarities between AIS(T) and the type strains of species of the genera Idiomarina and Aliidiomarina were 91.6-95.1 % and 94.0-96.9 %, respectively. The major isoprenoid quinone of AIS(T) was ubiquinone 8 (Q-8). Predominant cellular fatty acids were iso-C17 : 0, iso-C15 : 0 and summed feature 9. The genomic DNA G+C content was 45.8 mol%. It is concluded that AIS(T) represents a novel species of the genus Aliidiomarina, and the name Aliidiomarina shirensis sp. nov. is herein proposed for it. The type strain is AIS(T) (= JCM 17761(T) = BCRC 80327(T)). Based on its fatty acid profile and our phylogenetic analysis, we propose that Idiomarina maris be transferred to the genus Aliidiomarina.