In s earch f or bioactive c ompounds, 88 f ungal isolat es w ere c ollect ed from t hree Eg yptian marine habitats . Crud e extrac ts of 17 m arine derived fungal is olat es out of t he 88 isol at es show ed v ariable activit y ag ainst som e human pathogenic bac terial strai ns ( S almonella enterica, Prot eus sp., Klebs eilla pneumonia, Staphyloc occ us aureus and Escherichi a coli ). The m ost pot ent fungal isol at e that s howed the highes t antimicrobial activit y w as molec ularl y identified as As per gillus welwetsic hiae.Optimizati on of c ultur e conditions of A. wel wet sichi ae r evealed t hat the highest antimi cr obial activit y w as obtai ned in s haki ng c onditions (150rpm), using Czapek-dox medium, at pH 9 and incubation at 25°C f or 3 d ays. S almonella ent erica w as the most s ensitive t est organism regarding the highes t inhibition z one t hrough all the optimization tests. E thyl ac et at e extr act of A . welwetsic hiae w as s ubject ed t o c hemic al anal ysis and declar ed t hat t he activ e antibact erial m et abolite is a mi xtur e of acid (Mono (2-et hyl hexyl) pht halat e) and est er (bis (2-et hylhexyl) pht hal at e). Ret esti ng the tw o compounds s eparat el y, they s how ed no activit y whic h confirmed the s ynergistic antibact erial eff ect of t he two c ompounds toget her. Upon testing the c yt ot oxic eff ect of the active antibac terial m et abolit e (mixtur e of acid and ester) ag ains t human lung fibroblast norm al cell (W I-38 c ell line), t he res ults show ed t hat there w as a ver y w eak inhibitor y activit y s uggesting the possibility of considering it as a saf e c ompound f or f urther steps as a pharmac eutical prod uct. KEY WORDS: Marine derived f ungi , A ntimicrobial compounds, As per gillus CORRESP ONDENCE: