The drilling samples taken from the western part of the Bakırköy Basin were investigated, and the microplaeontological data were evaluated. Pliocene, Late Miocene and Late Eocene aged sediments have been observed from top to bottom of drilling, at the results of the laboratory investigation. 14 genera and 25 species from the ostracods and 10 genera and 8 species of benthic foraminifera from the Pliocene sediments: 6 genera and 11 species of ostracods, 9 genera 9 species of benthic foraminifera from the Late Miocene deposits and 11 genera and 11 sepices of ostracods and 20 genera and 6 species of benthic foraminifera from the Late Eocene sediments were described. The microfauna of Pliocene sediments consists of Cyprideis seminulum (Reuss), C. pannonica (Mehes), C.anatolica Bassiouni, C. torosa (Jones). C. tuberculata(Mehes). C. trituberculata Kristic. C. pontica Kristic are rare, and characteristic for Pontic Basin. In addition, Loxoconcha sp., Semicytherura sp.. Xestoleberis margaritae Mauller, X. ventricosa Mueller. X, reymenti Ruggieri, X. communis Mueller. Darwinula stevensoni (Brady&Robertson), D. cylindrica Straub. llyocypris cf., bradyi (Norman), Candona (Candona) altoides Petrovski. C. (Candona) parallela pannonica Zalanyi. C. (Candona) decimal Freels, C. (Candona) Candida (Müller). C. (Candona) neglecta Sars Heterocypris salina salina (Brady), Eucypris dulcifons Diebel & Pietrzenuik are found in the sequence, and foraminifera consisting of Siphonaperta aspera (d'Orbigny), Quinqueloculina seminula (Linne), Eponides concameratus (Williamson), Clbicidodies sp., Cibicides advenum (d'Orbigny), Asterigerina sp.. Ammonia compacta Hofker, A. parkinsoniana (d'Orbigny). Challengerella bradyi, Billman, Hottinger & Oesterle, Elphidium crispum (Linne) are of Pliocene age. The following species were identified from the Upper Miocene; these are respectively Cyprideis seminulum (Reuss), C. pannonica (Mehes), C. anatolica Bassiouni. C. torosa (Jones) C.pontica Krstic, Tyrrhenocythere triebeli Krstic, Xestoleberis ventricosa Mueller, X. reymenti Ruggieri. llyocypris cf. gibba (Ramdohr). Heterocypris salina salina (Brady) from the ostracods species and Quinqueloculina seminula (Linne). Q. cf. lamarckiana d'Orbigny, Quinqueloculina sp. 1, Quinqueloculina sp. 2, Cibicidoides sp, Eponides concameratus (Williamson). Lobatula (Walker & Jacobs), Ammonia compacta Hofker. A. parkinsoniana (d'Orbigny), Porosononion subgranosum (Egger). Elphidium crispum (Linne) from benthic foraminifera. Upper Eocene sediments contain following ostracods; Cytherella triestina Kollmann. Bairdia subdeltoidea (Muenster), B. elongata Lienenklaus, B. cymbula Deltel, B. crebra Deltel, Bairdoppilata cf. gliberti Keij, Triebelina punctata Deltel, Schizocythere appendiculata appendiculata Triebel, S. tessellata tessellata (Bosquet). Eucythere sp. 1, Eucythere sp. 2, Thracella apostolescui Sönmez, Krithe rutoti Keij, Echinocythereis isabenana Oertli. Leguminocythereis genappensis Keij, Nucleolina multicostata (Deltel), Pokornyella osnabrugensis (Lienenklaus). P. ventricosa (Bosquet), Hermanites paijenborchiana Keij, H. triebeli Stchepinsky, Quadracythere vermiculata (Bosquet). Q. hulusü SönmezG6k9en. Cytheretta tenuistriata (Reuss), C. bartonica Sönmez-Gökçen. Xestoleberis sublobosa (Bosquet). X. muelleriana Lienenklaus, Uroleberis sp., Paracypris contracta (Jones) Among the foraminifera Halkyardia minima (Liebus), Sphaerogypsina globula (Reuss). Asterigerina rotula (Kaufmann), Chapmanina gassinensis (Silvestri), Nummulites fabianii (Prever), N. striatus (Bruguiere) are characteristic for this level. According to result of the drilling samples taken from the western part of the Bakırköy and Ataköy region, it is indicated that there were the restricted environments, and that salinity reduces depending on the shallowness in Late Miocene and shallow marine in Late Eocene in the region. In addition, it is observed that it changed to lagoonal and shallow marine in the Pliocene.