This dataset contains osmium isotope ratios and osmium and rhenium concentrations from mudstone samples collected from the low-resolution interval of the Kawaruppu section, Nemuro Group, Hokkaido, Japan. The data cover the Upper Cretaceous-lower Paleogene interval across the Cretaceous-Paleogene boundary and were compiled for an integrated stratigraphic investigation of the boundary interval. Osmium isotope ratios and Os concentrations were measured by negative thermal ionization mass spectrometry (N-TIMS; TRITON, Thermo Fisher Scientific) and rhenium concentrations were measured by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS; iCAP Q, ThermoFisher Scientific) at Japan Agency for Marine-Earth Science and Technology (JAMSTEC).