A total of 21 ant species belonging to 11 genera in four subfamilies was collected from the Oki Islands. This corresponded to 23.9% of 88 species collected so far from Shimane Prefecture. The most species (19) were collected from Saigo Port. The average of the ant species collected at 6 ports was 13.7. The dominant ant species estimated by the ratio of occurrence to all of the honey baits (180) was Tetramorium tsushimae (0.45), followed by Formica sp. B (0.41), Temnothrax spinosior (0.14) and Camponotus japonicus (0.11). The similarity of species composition calculated by Nomura-Simpson’s Coefficient (NSC) was the largest (1.00) between Saigo Port and Beppu and Urago ports, and was the smallest (0.67) between Shibaura and Nifuri ports. In this study, no alien ant species was collected from the Oki Islands. Monomorium chinense was collected for the first time in Shimane Prefecture. A difference of similarity in species composition among nine regions so far surveyed in southern Japan was found between the Northern and Middle Ryukyus.