From a hexane extract of the tunicate Cynthia savignyi, collected in Morocco, epidioxysterol or 5,8-alpha-epidioxy-5alpha-cholest-6-en-3beta-ol has been isolated. This is the first example of epidioxysterol found in the tunicate C. savignyi. The structure of epidioxysterol has been characterised by NMR data (1H, 13C and 2D). Epidioxysterol possesses antifungal activity against three tomato pathogenic fungi: Botrytis cinerea, Fusarium oxysporum and Verticillium albo atrum and antibacterial activity against Agrobacterium tumefaciens, Escherichia coli, Staphylococcusfaecalis, Staphylococcus aureus and Pseudomonas aeruginosa and cytotoxicity against Artemia salina larvae.