This dataset contains osmium isotope ratios and platinum group element concentrations from the high-resolution interval of the Kawaruppu section, Nemuro Group, Hokkaido, Japan. This interval represents an approximately 15 m thick subset of the low-resolution interval and was sampled at 10–20 cm spacing to investigate the stratigraphic interval expected to contain the Cretaceous-Paleogene boundary. The dataset consists mainly of mudstone samples and also includes one calcareous vein sample and one tuff sample. Osmium isotope ratios and Os concentrations were measured by negative thermal ionization mass spectrometry (N-TIMS; TRITON, Thermo Fisher Scientific) and rhenium and other platinum group 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).