Hysterothylacium species are the most prevalent ascaridoid nematode reported from various freshwater, estuarial and marine fish species. However, there are very few studies about molecular identification and characterization of Hysterothylacium species in marine fish species from Turkish waters. The aim of the present study was to molecular identification and characterization of Hysterothylacium larvae from Boops boops caught off Aegean Sea, Turkey.Hysterothylacium larvae were found in 10 of 109 B.boops. The prevalence of Hysterothylacium spp. larvae was 9.2%. A total of 10 larvae of Hysterothylacium spp. were collected from all infected fish. Hysterothylacium larvae were genetically identified as H.aduncum, H.fabri and H.reliquens from Turkish waters by using sequence analyses of rDNA ITS regions in B.boops for the first time. In addition, B.boops was reported as a new host for H.rehquens Moreover, H.rehquens was characterized for the first time by sequencing of the ITS regions from the Turkish waters with the present study.