Nine new acetylenic alcohols 1-9 were isolated from a marine sponge belonging to the genus Petrosia (Strongylophora). The structures were elucidated mainly based on the analysis of one-and two-dimensional NMR spectral data. To determine the position of the central double bonds in 1-8, each compound was cleaved with OsO(4) and HIO(4), and the resulting aldehyde was converted to the corresponding 2,4-dinitrophenylhydrazone. Analysis of the high-resolution mass and (13)C NMR spectral data of each 2,4-dinitrophenylhydrazone clarified the position of the central double bonds in 1-8.