Spatial and temporal distributions of polychaetes inhabiting the Gediz River Delta were studied seasonally at 11 stations during summer 1998 - spring 1999. A total of 83 species belonging to 31 families were encountered, of which Micronephthys maryae San Martín, 1982, Prionospio multibranchiata Berkeley, 1927 and Aricidea claudiae Laubier, 1967 were new records for the Turkish fauna. Among the families, Spionidae ranked first in terms of number of species (14 species, 17% of the total number of species) and individuals (3922 individuals, 48% of the total number of individuals). The Gediz River Delta was mainly dominated by Capitella capitata (Fabricius, 1780), Polydora ciliata (Johnston, 1838), Streblospio shrubsolii (Buchanan, 1890), Spio decoratus Bobretzky, 1870, Heteromastus filiformis (Claparede, 1864) and Hediste diversicolor (O. F. Müller, 1776). Species assemblages in the area and variations in community indices at stations with respect to seasons were determined and discussed.