This study on the species composition and distribution of tintinnids, which form one of the most abundant ciliate groups in the seas, was carried out in Büyükçekmece Bay in 1998-1999. Plankton samples were collected horizontally from the subsurface (0.5 m) with a 55 µm plankton net at five stations and a 3 l water sampler was used for their quantitative analysis. All tintinnid species were identified according to their lorica shape as the usual important criterion. A total of 14 species were identified. Primary hydrographic conditions such as salinity, temperature and dissolved oxygen were recorded on each sampling occasion. The genera Favella and Eutintinnus were dominant in terms of species and individual numbers. Eutintinnus fraknoi was the most abundant species, with a mean abundance of 0.4x10³ ind. l^-1. The study shows that the species and individual numbers of tintinnids decreased in winter and early spring when phytoplankton increases. The abundance of tintinnids in Büyükçekmece Bay appears to be correlated with the decrease in abundance of total phytoplankton (r_s= -0.57, p= 0.05) and diatoms (r_s= -0.65, p<0.05) and the increase in temperature (r_s= 0.61, p<0.05). Furthermore, phytoplankton abundance was positively correlated to dissolved oxygen (r_s= 0.64, p<0.05). In particular, Favella serrata was more affected by temperature and Eutintinnus lusus-undae by salinity compared to other species.