Conodont apatite from a shallow-marine Middle Devonian transgressive unit has been investigated in five borehole sections representative of the epicontinental Belarussian Basin located in a near-equatorial setting. The transgression is related to the onset of the late Eifelian Kačák Event, an important biotic episode recorded worldwide. The δ18Oapatite data were acquired using the secondary ion mass spectrometry (SHRIMP) technique. The mean corrected values in the studied sections are in the range 19.8 ‰ to 20.2 ‰, significantly exceeding the values measured for late Eifelian low-latitude open marine basins. This can be explained by higher average δ18Oseawater levels related to elevated seawater salinities in the Belarussian epeiric basin, in agreement with the presence of impoverished marine fauna. The intra-specimen δ18O variability, with differences ranging up to 2.6 ‰ in some specimens, can be explained by fluctuating δ18Oseawater and, to a smaller degree, temperature variations in the Belarussian inland sea under a monsoonal climate. The present results demonstrate that local paleoclimate and epeiric paleogeography may considerably obscure the global climatic signature of the conodont apatite isotopic record.