This paper deals with the sipunculan species collected from 17 stations between 15 and 70 m depths in the Aegean and Levantine Seas. A total of eight sipunculan species were found in the area, six species in the Aegean Sea and four species in the Levantine Sea. The population densities of sipunculans at stations ranged from 10 to 300 ind.m(-2). The maximum density was estimated to be 160 ind.m(-2) in the Aegean Sea and 300 ind.m(-2) in the Levantine Sea. The most dominant species in the area was Onchnesoma steenstrupii steenstrupii, comprising 84.1 and 89.4% of the total number of specimens in the Aegean and Levantine Seas, respectively. Two major sipunculan assemblages were found in the area and the main environmental factors controlling these assemblages were depth, sediment grain size and the concentration of orthophosphate-phosphorus. Pearson correlations between abundances of the eight sipunculan species and abiotic variables indicated that the number of individuals of Phascolion (Phascolion) strombus strombus and Sipunculus (Sipunculus) nudus were significantly correlated with the gravel and coarse sand percentages of the sediment. The present study included two alien sipunculan species; Apionsoma (Apionsoma) misakianum and Aspidosiphon (Aspidosiphon) mexicanus in the Levantine Sea. Brief descriptions of the species and their distributional characteristics are given.