A phytosociological study of the phytobenthos was carried out along the coast of Lebanon during 1996-97. Samples were collected seasonally at six sites, some of which showed distinct pollution signature. Quadrates of 0.04 m-2 were taken at selected stations fixed on transects perpendicular to the rocky shore and covering the supralittoral, the mediolittoral and infralittoral zones. The taxonomic composition, the abundance and species diversity of algal community were analysed in relation to environmental factors. A total of 230 taxa were identified during the period of survey. Several sources of pollution, resulted in the reduction of macroalgae biomass and of the taxonomic diversity. Several Indo-Pacific species were found within the different phytocoenoses of the area; most of them were introduced into the Levantine Basin through the Suez Canal. These species, that were introduced into the Eastern Mediterranean, formed permanent populations; some of them were highly spread and dominated over other endemic species or even they replaced them.