ABSTRACT: The Kayikoy Formation (Isparta, SW Turkiye) consisting of sandstone, claystone, and marl units contains abundant, low-moderate preserved, and diverse planktonic foraminifera assemblages. Eight planktonic foraminiferal biozones (E9-E16) were determined encompassing the Lutetian-Priabonian stages (middle-upper Eocene) by using the biostratigraphic distributions of 17 genera and 62 species of planktonic foraminifera. Stable delta 18O and delta 13C isotope values were measured for 53 individuals belonging to Morozovelloides crassatus, Acarinina bullbrooki, A. topilensis, A. echinata, Globigerinatheka curryi, G. index, G. subconglobata, G. mexicana, G. barri, G. euganea, Orbulinoides beckmanni, Turborotalia frontosa, T. pomeroli, Hantkeninamexicana, H. liebusi, H. dumblei, H. alabamensis, and Dentoglobigerina eotripartita. By integrating planktonic foraminiferal biostratigraphy, stable delta 18O and delta 13C isotopes, and paleotemperature analyses, the first detailed study of the Middle Eocene Climatic Optimum (MECO) record was performed in SW Anatolia/Turkiye. The overall signature of the MECO is similar to global observations but also involves some regional differences. The MECO paleotemperatures, determined to vary between approximately 2 degrees C and 5 degrees C, were similar to the global records, but the slight differences in values in the three sections are most likely due to the paleogeographic position of the studied section in Turkiye.