Seaweed extracts in different solvents exhibited different antimicrobial activities.Solvents like methanol, ethanol, chloroform or a mixture of these are widely used to extract active princples from living organisms. No specific solvent exhibited activity against all the test organisms effectively. In the present study the marine algae Ulva sp was tested for its antimicrobial properties against six pathogenic bacteria. There was activity in all the three solvent systems used. All the algal extracts investigated, showed activity against Pseudomonas fluorescens.