Bioethanol is made by the fermentation of biomass and different from petroleum-derived ethanol. The Korean government started a two year long feasibility study of using bioethanol mixed with sub-octane gasoline as transportation fuel in 2006. The development of analysis methods for bioethanol is an urgent issue to protect illegal circulation of synthetic ethanol in the transportation fuel market. In this letter, a new approach was introduced to analyze bioethanol and synthetic ethanol within a mixture of sub-octane gasoline and synthetic ethanol using low level liquid scintillation counting (LSC).