During the course of our investigation for isolation of biological active compounds from marine organisms of the Turkish seas, secondary metabolites and bioactivities of, Microcosmus vulgaris collected from (Turkish coasts) Izmir coast was studied. In the study 5 alpha - 6 alpha - epoxyergosta 7-en- 3 beta- ol was isolated from Microcosmus vulgaris. Furthermore, antioxidant and antiproliferative activity of crude extract and 5 alpha- 6 alpha-epoxyergosta 7-en- 3 beta- ol were determined by DPPH, superoxide radical scavenging and nitric oxide radical scavenging and MTT assay respectively. Antimicrobial activity of crude extract was also determined against some Gram positive, Gram negative and yeast strains. Stearic acid, palmitic acid and myristic acid were also detected by GC-MASS analysis. This is the first study about isolation and bioactivity determination of Turkish M. vulgaris.