Seasonal physicochemical analysis of sea water and epiphytic diatoms at Suez Canal (3 sites), Gulf of Suez (3 sites) and Red Sea coast of Egypt (6 sites) indicated that nutritional status of water (nitrogen, phosphorus and silicon) decreased sharply downward (from Qantara to Marsa Alam). Meanwhile, the surface water salinity and water temperature increased. The total annual number of epiphytic diatom species decreased gradually from Qantara (48 species) towards El-Sharm (15 species). The most frequent diatom species belonging to genera Navicula, Cynedra, Achnanthes, Eunotia, Diatoma, Cocconeis, Cymbella, Licmophora, fragilaria, Amphora and Melosira. The maximum growth of epiphytic diatom (cell number and biomass) was recorded during summer, while the minimum during winter. A dendrogram of diatom communities resulted in five clusters according to temporal and trophic status of water. Water samples were mesoeutrophic at Ras Ghareib, Fayeid and Qantara during summer, with Generic Diatom Index (GDI) equals 11-12. Most water samples of cluster I and II were oligo-mesotrophic (GDIequals12-14) during spring and autumn. Oligotrophic water (GDI>14) were recorded in samples belongs to clusters IV and V while most samples are related to cluster III.