Stable hydrogen and oxygen isotopic compositions (δD and δ18 O values, respectively) were analyzed for "sake," a traditional Japanese alcohol beverage, to assess these values for the identification of its geographic origin. We collected sake (Junmai-shu; made of only rice, water, and koji) and its source water (i.e., brewing water) from breweries in Niigata Prefecture, Japan, and measured the isotopic compositions of water in these samples. The δD and δ
18O values for the sake are well correlated with their respective values for the corresponding brewing water (δD; r = 0.92, δ 18 O; r = 0.80). Furthermore, based on the δD-δ 18 O cross plot, sake brewed in Niigata Prefecture is distinguishable from that brewed in countries other than Japan. These results imply that this dual isotope (δD and δ 18 O) analysis is potentially useful in identifying the geographic origin of sake.