The coastal fish assemblage in the marine park of the Ustica Island was studied using underwater visual census. Seasonal surveys were conducted from May 1996 to March 1997 at several sites located within three zones of the reserve, each characterized by different levels of protection (integral reserve, general reserve and partial reserve). Visual strip transects were conducted using SCUBA at three different depth (3–5 m; 10–15 m; 25–30 m). Species richness and diversity indices were better correlated to depth than to protection level. Oppositely, size and/or abundance of some vulnerable species (e.g.,Epinephelus marginatus, Labnis me‐rula, Labrus viridis)were positively correlated with degree of protection and the so‐called ‘reserve effect’. These observations stress the importance of protection measures for littoral fish assemblages and represent the only available data for an Italian marine park of considerable extent.