Abstract: Molluscan assemblages have been formed determining that the surface sediments of the Marmara Sea taken by grab method haddifferent fauna compositions showing different environmental features during Late Quaternary. According to this, the first assemblage represents Neoeuxinian (upper most Pleistocene) having a salinity of 2-8 %o on a gravel dominant base and it was formed mainlyby species such as Dreissena rostriformis distincta And., Lithoglyphus naticoides (C. Pfeif.), Hydrobia (Hydrobia) ventrosa (Mont.),Micromelania caspia lincta Mil.. During this period the sea level of the Marmara sea was at least 28 m. lower than that of today whichwas probably the sill depth where the Holocene transgression initiated. Later, the salinity of the environment increased a little due tothe Mediterranean transgression during Early Holocene and brackish water-marine environment conditions were formed (10 %o18%o salinity). The second molluscan assemblage which represents the above mentioned environment was formed mainly by eury haline marine species such as Rissoa (Rissoa) splendida (Eichw.), Parvicardium exiguum Gm., Cerastoderma (Cerastoderma) edule (L.).This period lasted shortly; Typical Mediterranean fauna comprising numerous species such as Jujubinus striatus (L.), Turritella (Turritella) tricarinata (Brocc.), Chrysallida (Parthenina) excavata (Phill.), Trunculariopsis truncula (L.) etc. became dominant due to theaccelerated transgression during Late Holocene, and consequently today`s conditions of the Sea of Marmara were formed. So thethird molluscan assemblage living in salinity varying from 18%o to 35%o was formed belonging to above mentioned period and wasdivided in  3 sub-groups according to lithology and depth.