The size variation, growth pattern, sex ratio, fertility, and spawning of three nereidid polychaetes from Egyptian coasts were studied for a complete year, namely Perinereis cultrifera (Grube 1840), Perinereis nuntia (Grube 1857), and Platynereis dumerilii (Audouin and Milne-Edwards, 1833). The results revealed clear monthly variation in the studied parameters, and the three species showed allometric growth, while P. cultrifera displayed both allometric and isometric growth. Perinereisnuntiawas characterized by the greatest size, the highest percentage of maturation, the highest fecundity, and the largest oocyte diameter. Perinereis cultrifera and P. dumerilii had a close maximum length of 6.5 and 7.4 cm respectively. However, P. cultrifera displayed pronouncedly lower fecundity and maturation percentage than P. dumerilii, while the latter species recorded less biomass and smaller oocytes. In addition, the spawning of the three species occurred in different months of late spring and early summer, being in May-June for P. cultrifera, June-July for P. dumerilii, and March-April for P. nuntia..