From collected data analyzed to produce an inventory of all polychaetes in Algerian waters, the diversity of this group was estimated as 534 species. The largest families are Syllidae (66 species), Spionidae (37 species) and Terebellidae (27 species). The presence of those listed species along the Algerian coast was compared with their occurrence in nine other areas of the Mediter-ranean Sea, in the Black Sea and in four other more distant seas around the world. Comparisons are also made with respect to the biogeographical origin for each species. The polychaete fauna of the Algerian coast is among the richest of the Mediterranean Sea and comparable to the diversity reported for the French Mediterranean continental shelf and that in the Aegean Sea, but higher that that found in the nearby coastlines of Morocco and Tunisia. Most of the species found have an Atlantic origin and are present in the western Mediterranean Sea. This current inventory includes eight non-indigenous polychaete species found in the Algerian waters.