Abstract Lead (Pb) isotopes are powerful tools for tracing dust provenance and reconstructing paleoclimate. However, variations in Pb isotopic compositions among different grain‐size fractions in sediments complicate their use. We examine the Nd‐Pb isotopic compositions of two sediment fractions (<2 μm and 30–63 μm) from the central Japan Sea during the last glaciation (26–12 ka BP). Our results indicate that these sediments primarily consist of aeolian dust transported by the East Asian Winter Monsoon. The <2 μm fraction exhibits more radiogenic Pb isotopes than the 30–63 μm fraction. This size‐dependent discrepancy in Pb isotopes is attributed to differences in sediment composition, governed by the incongruent weathering of minerals in source rocks and transport sorting. Comparisons of dust records from inland and marine archives reveal contrasting mechanisms that control Pb isotopic compositions. We propose that greater caution is necessary when using Pb isotopes in paleoclimatology and paleoceanography.