Abstract: In this study, the aim was to reveal the palaeoecological and palaeoclimatic characteristics of the sediments around the Beysehir Lake basin, along with the gastropod fauna. As a result of the examination of samples taken from sediments from the Ancient Beyşehir Lake, 13 genera and 15 species belonging to the Gastropoda class of the Mollusk branch were identified. When the fauna was evaluated in terms of numerical abundance, the typical dominant species were Valvata pulchella living in rivers and Bithynia leachii living in shallow freshwater. It is thought thatthe lake was a freshwater environment fed by rivers during the time period when levels where Bithynia leachii and Valvata pulchella species were deposited together. In the time interval when Valvata pulchella and Bithynia leachiispecies decreased and species living in marsh and stagnant water environments such as Planorbis planorbis, Anisusvortex, and Gyraulus parvus increased numerically, the environmental conditions indicate temperate, very shallow, closed lake conditions. Valvata beysehirensis, which is an endemic species in the Ancient Beysehir Lake indicatinga freshwater environment fed by rivers, was observed at many levels of the basin. The presence of V. beysehirensisspecies, which was dated to the late Pleistocene in the literature, during the Pleistocene was revealed in this study.When the ESR dating results, ages determined by other researchers and palaeoecological characteristics of theidentified fauna are evaluated together, 7 arid and 6 wet climatic periods were effective in the study area during thePleistocene. The climatic conditions in the study area are compatible with the palaeoclimatic changes between MIS16-MIS 2 phases, which show global sea level changes in the last 659 thousand years.