Species composition, abundance, and monthly distribution of mollusk fauna as well as physical and chemical variables of Aksu River were investigated from February 2003 to July 2004. Mollusk fauna in Aksu River was represented by 10 taxa of Gastropoda and 3 taxa of Bivalvia. Aksu River contains four different water quality regions among the stations as unpolluted (E1), slightly polluted (E2, C1, C2, A1, Ak1, Ak2), moderately polluted (C3, Ak3), and highly polluted (I1, I2). Only Pisidium sp. was found at the unpolluted station El. Ancylus fluviatilis (O. F. Muller, 1774), Pisidium sp., Oxyloma elegans (Risso, 1826), and Melanopsis praemorsa (Linnaeus, 1758) were found to be dominant at slightly polluted stations. Valvata piscinalis (O. F. Muller, 1774) and Physa acuta (Draparnaud, 1805) predominated at moderately polluted stations. Only Physa acuta was found at highly polluted station I2. No mollusk specimens were observed at highly polluted station I1 It was also observed that Physa acuta and Radix labiata (Rossmassler, 1835) can tolerate high levels of BOD(5), NH(3)-N, NH(4)-N, Cl and PO(4)-P but low DO levels.