The northwestern part of the Black Sea is a vast shallow water area, whose biocenoses are an important part of the Black Sea ecosystem. Since the benthos of this region has not been studied in recent decades, data about its current state are actual. A significant contribution to the taxonomic composition of macrozoobenthos is made by polychaetes of the family Spionidae, which are represented by a large number of species and are characterized by high abundance rates. The aim of the research is to study the species composition, distribution and quantitative development of polychaetes of the family Spionidae in the northwestern part of the Black Sea at depths of more than 10–15 m. The material used was macrozoobenthos samples collected from 160 stations in the cruise of the R/V "Maria S. Merian" and the R/V “Professor Vodianitsky” in 2010–2017 at depths from 10 to 137 meters. Bottom sediments were collected using the “Ocean-25” bottom grab (0.25 m2 capture area) and box corer (S=0.1 m2). The bottom soil was washed through sieves with the smallest diameter of 1 mm. 230 samples were collected and processed from 160 stations. 83 species of Polychaeta, including 12 Spionidae, were found on the inhabited part of the shelf of the northwestern part of the Black Sea. Polychaetes were recorded at all the stations performed, spionids – at 66 % of their total number. Up to 6 spionid species have been recorded at singl stations, with an average of 2–3 species at the station. 11 species have been identified: Aonides paucibranchiata Southern, 1914, Dipolydora quadrilobata (Jacobi, 1883), Microspio mecznikowianus (Claparède, 1869), Prionospio cf. cirrifera Wiren, 1883, Polydora cornuta Bosc, 1802, Pygospio elegans Claparède, 1863, Scolelepis (Parascolelepis) tridentata (Southern, 1914), Scolelepis (Scolelepis) cantabra (Rioja, 1918), Spio decorata Bobretzky, 1871, Laonice cf. cirrata (M. Sars, 1851), Marenzelleria neglecta Sikorski & Bick, 2004. Non-identified specimens of genus Prionospio also have been registered. The distribution of Spionidae in the water area of the north-western part of the Black Sea is uneven, which is due to the reaction of individual species to various environmental factors. 230 samples were collected and processed from 160 stations. The maximum density of Spionidae reached 2984 ind.∙m-2, averaging 477±126 ind.∙m-2. The highest density of spionids was observed in the depth range of 20–40 m. P. cf. cirrifera, A. paucibranchiata, and D. quadrilobata dominated in density. Three of the identified species, (M. neglecta, P. cornuta, and D. quadrilobata) are invaders in the Black Sea. In the taxonomic composition of Polychaeta, Spionidae are accounted for 14%, while in the quantitative development their contribution reached 42 % of the total density of Polychaeta, which indicates the significant role of this family in the functioning of the bottom ecosystem of the northwestern part of the Black Sea.