Stable carbon and oxygen isotopic compositions (_13C and _18O) of benthicforaminiferal carbonate shells have been used to reconstruct past bottom water environments.However, the details of factors controlling the isotopic disequilibrium be-5 tween the shells and the surrounding bottom seawater (the vital effect) are still ambiguous.In this study, we analyzed the isotopic composition of individual benthicforaminifera of multiple species by using a customized high-precision analytical system,and found that the magnitude of the vital effect in different species is correlated withinter-individual variations. As a result, we can choose suitable species as bottom water10 proxies by using the inter-individual isotopic variations. In addition, by using the simplifiedinterpretation of the vital effect established in this study, we can reconstruct the_13C values of dissolved inorganic carbon in bottom water by correcting foraminiferalisotopic compositions for the isotopic shift resulting from the vital effect. Our findingswill allow the use of isotope data for all benthic foraminifera as more reliable proxies for15 reconstructing past bottom water conditions and evaluating global carbon cycling.