The blue-green algal virus LPP-1 was concentrated by ultrafiltration and purified by density-gradient and differential centrifugation. The virus contains DNA and has a sedimentation coefficient of 548S. Electron micrographs of purified viral preparations show that the polyhedral particles have short tails, which are approximately one-fourth as long as the diameter of the head. Data presented in this report indicate that the blue-green algal virus more closely resembles bacteriophages than viruses infecting higher plants.