From the dichloromethane extract of the marine green alga Ulva fasciata Delile, collected from the Mediterranean coast of Egypt, three new fatty acids, namely, (E)-11-oxo-octadeca-12-enoic acid (1a), (E)-11-hydroxy-octadeca-12-enoic acid (2a) and 6-hydroxy-oct-7-enoic acid (3a) together with cholesterol were isolated. Analysis of the unpolar part of the extract using GC-MS detected the existence of further ten compounds, namely, dimethylsulfoxide, dimethylsulfone, phenylacetamide, 6,10,14-trimethyl-pentadecan-2-one, 8-heptadecene, dodecane, tridecane, 4-oxo-pentanoic acid, hexadecanoic acid, and the naturally new 1,1 -bicyclohexyl. Structures of the isolated compounds 1a -3a were confirmed by spectroscopic analyses including mass spectra (EI-MS, HR/ESI-MS), 1D and 2D NMR experiments, and by the synthetic conversion into their corresponding methyl esters 1b -3b. The algal extract and its components were comparatively examined against several pathogenic microorganisms, and brine shrimps for cytotoxicity.