To identify the mollusk fauna of Istranca Stream, samples were collected seasonally from 18 stations from September 2011 to August 2012. The mollusk fauna of the stream consists of a total of 14 species, 11 of which belong to Gastropoda: Theodoxus (Theodoxus) fluviatilis (Linnaeus 1758), Bithynia tentaculata (Linnaeus 1758), Bithynia pesicii Gloer & Yildirim 2006, Bithynia pseudemmerica Schutt 1964, Valvata naticina Menke 1845, Valvata piscinalis (Muller 1774), Galba (Galba) truncatula (O F Muller 1774), Radix labiata (Rossmassler 1835), Physella acuta (Draparnaud 1805), Planorbis (Planorbis) planorbis (Linnaeus 1758), Oxyloma elegans (Risso 1826); three of which belong to Bivalvia: Pisidium casertanum (Poli 1791), Anodonta cygnea (Linnaeus 1758), Unio pictorum (Linnaeus 1758). Futhermore, water temperature (inverted perpendicular C), pH, nitrate nitrogen (NO3--N), nitrite nitrogen (NO2--N), and phosphate (PO4--P) of each sample were measured at the sampling sites. The relationships of species to environmental parameters were reviewed by CCA analysis. This research is the first study conducted on the Istranca stream to determine the mollusk fauna.