T The Banggai Sea, Central Sulawesi is an important area for paleooseanographic research in Indonesia. As part of the Indonesian Throughflow (ITF), this region experiences significant upwelling phenomena influenced by the seasonal monsoon cycle. This study aims to reconstruct past aquatic conditions in the Banggai Sea by analyzing the abundance of upwelling nanofossils in sediment cores collected during the “Banggai Upwelling Dynamics and Ecosystem Experiment” (BUDEE) 2022 research expedition under the National Research and Innovation Agency (BRIN). Nanofossils of 26 genera and 45 species, mainly Florisphaera profunda, Gephyrocapsa oceanica, and Reticulofenestra spp., were identified and analyzed using polarizing microscopy. The abundance of coeval nanofossils along the sediment core showed significant changes between species from the lower photic zone and the upper photic zone, indicating changes in sea level conditions in the Banggai Sea through time. The number of specimens per gram of sediment shows an inverse correlation with the abundance of Florisphaera profunda (%Fp) and the occurrence of assemblage fossils, supported by the size distribution of Gephyrocapsa oceanica species as a characteristic species of the shallow photic zone. Produced paleseanographic reconstructions showing oligotrophic and eutrophic water conditions influenced by upwelling phenomena during the eastern monsoon and sediment material input from the river.