Remarkable variation was observed for substrate composition distribution between both inside and outside territories of the surgeon fish Acanthurus sohal on reefs of Ras Mohamed National Park, South Sinai, and Egypt. Eight genera of hard corals were recorded; Acropora, Favites, Pocillipora and Stylophora were the dominant and the widespread genera inside the A. sohal territory. On other hand, the Acropora, Pocillipora, Stylophora and Porites were the dominant and the widespread genera outside the A. sohal territory. Five soft coral genera; Sinularia, Sarcophyton, Xenia, Dendrophyllia and Nephthyia were recorded inside and outside the territories of A. sohal. The difference was very clear in algal composition between inside and outside territory. Filamentous algae were dominant inside the territory, while it was not dominant outside the territory. Three groups of associated fauna (Mollusca, echinoderms and sponges) were recorded in the study area outside the territory, while two groups (Mollusca and sponges) were recorded inside the territories. Dead component of substrate (old reef, sand, rubbles and others) showed dominance outside the territory more than inside. The percentage covers of algae, especially filamentous algae, had the highest values inside territory. The total territory areas of A. sohal varied between 12.8 m2 and 17.0 m2, by an average 15.2 m2 in the whole study area. There was a significant positive correlated relationship between surgeon fish A. sohal territory size and the complexity of substrate inside the territory