Purification, characterization and initial identification of extracellular algae-lysing constituents of fermentation products of the algicidal bacteria S7 are carried out by ultraviolet spectrum, infrared spectrum, fluorescence spectra and mass spectrum, and the results show that the eluates of methanol have the best algicidal effects. These active algicidal substances made of conjugation unsatuated bonds, hydroxyl, saturated alkyl and aromatic ethers. In the three-dimensional fluorescence spectroscopy, two strong fluorescence peaks appear at 264/436 nm and 378/369 nm respectively. Mass spectrum indicates that the active substances consist of six monomers, and their molecular weights are 163.1, 246.3, 274.3, 318.3， 404.5 and 475.4, respectively.