Osteological characteristics of skull, shoulder girdle, pelvic girdle, vertebrae, and pterygiophore of the four members of the genus Acanthogobius are described and compared. Characteristics of the metaterygoid, branchiostegals, urohyal, scapular, and pterygiophores that have been used to classify gobioid fishes were not different between the four species. However, ossification of the lacrymal and the number of ossified gill rakers differ from one Acanthogobius species to another. A. flavimanus is distinguished from its congeners in the size of the medial ethmoid, the number of caudal vertebrae, and the distance from left to right lateral ethmoid. A. lactipes has a large basihyal, and A. luridus has a wide distance from left to right lateral ethmoid: these are among the unique characters that distinguish them from other members of the genus. A. elongata differs notably from its congeners in the number of premaxillary and dentary teeth, the shape of the epural, and the length of the cranium.