Algae are known to produce a wide variety of bioactive secondary metabolites and several compounds have been derived from them with potential for use in the development of new pharmaceutical agents. In this study Chlorella vulgaris, Nannochloropsis oculata and Amphora coffeaeformis were examined for their antimicrobial activity. Methanol extracts of the selected algae were assayed for antimicrobial activity against Pseudomonas aeruginosa, Proteus vulgaris and Escherichia coli as Gram negative bacteria and Staphylococcus aureus, Bacillus subtilis and Streptococcus mutans as Gram positive bacteria. The used fungi were Aspregillus niger, Penicillium expansum and Syncephalastrum racemosum and one examined yeast was Candida albicans. Results indicated that Nannochloropsis oculata methanol crude extract showed the highest activity against bacteria while Chlorella vulgaris methanol crude extract showing the highest activity against fungi and yeast. Moreover, the crude extracts obtained were assayed for cytotoxicity against human Hepatocellular cancer cell line.  The active compound was identified by the GC-mass.