We demonstrated a novel identification method of illegal diesel fuel by using a deuterium (D) labeled n-alkane ([1-D] n-alkane) as a new chemical marker instead of coumarin. In a mixing system of diesel fuel with marker-labeled kerosene, kerosene content is quantitatively determined by D-enrichment of a target n-alkane in a mixed oil using compound-specific stable hydrogen isotope analysis. Thus, [1-D] n-alkane will become a high potential chemical marker instead of coumarin.