We report the isolation and structural characterization of an octaneselenolate-protected Au-25 cluster ([Au-25(SeC8H17)(18)](-)). Isolated [Au-25(SeC8H17)(18)](-) was characterized by various analytical techniques. The results strongly suggest that [Au-25(SeC8H17)(18)](-) possesses a similar geometric structure to the well-studied thiolate (RS)-protected Au-25 duster ([Au-25(SR)(18)](-)) and that the charge transfer between the metal atoms and ligands in [Au-25(SeC8H17)(18)](-) is lower than that in [Au-25(SR)(18)](-). To the best of our knowledge, this is the first report of the isolation of a selenolate-protected gold duster. [Au-25(SeC8H17)(18)](-) is an ideal compound for determining how changing the ligand from thiolate to selenolate affects the fundamental properties of a cluster.