Hydrophilic and lipophilic extracts were prepared from 8 microalgal strains, and screened for antimicrobial and antitumor activities. Antimicrobial activity was determined by observing bacterial （ S. aureus, Bacillus subtilis and Escherichia coh~ and fungal（Aspergillus niger and Penicillium chrysogenum） growth inhibition. All the microalgae had different degrees of antimicrobial activity against one or more microbe - tested, and 56.47% of the extracts showing the anti-S.aureus activity exhibited the antibacterial activity against （MRSA）. Cytotoxic activities were measured in vitro against human cancer cell lines HeLa by the MTT assay. Most of these extracts showed potent activity against the growth of the tumor cells, especially the intracellular lipophilic extracts from Isochrysis galbana Parke 3011 and Isochrysis galbana Parke H29, which exhibited strong antitumor activity against HeLa cell lines. The overall results of this study indicate that the extracts from microalgae represent a potential sources of medicine for the treatment of infectious and cancer diseases.
