Abstract: This paper describes a fossil fish specimen collected from the Lower Devonian near Yongfu,Guangxi. According to the outline of the head roof and features of endocranium,it is ascribed to Arthrodira. The width of the head roof is greater than the length of the post- pineal unit. The endocranium is divided into two parts,an ethemoidal region and a postethmo- occipital region. There are four lateral endocranium processes,namely,antorbital,supraorbital,anterior and posterior postor- bital processes,which are in keeping with those of Buchanosteus. So the new material ought to be ascribed to Buchanosteus. But the larger and dorso- laterally facing orbits, fine tubercular ornaments without fine radiating ridges on its cap and root are distinct from the features of B. confertituberculatus (Chapman). Thus the new material represents a new species of Buchanos- teus,that is B. guangxiensis sp. nov. The paper also discusses the paleogeographic relation between South China and Australia.