Ophiopogon japonicus is a herbaceous perennial plant in Liliaceae, and its tubers are used in traditional Japanese medicine as Bakumondo (麦門冬), prescribed for treating cough, sputum, and thirst. Liriope is a genus of ornamental plants related to Ophiopogon, and its tubers are used in folk medicine as well. Although tubers from both genera are traded in Korean and Chinese markets, only O. japonicus is defined as the plant of origin for Bakumondo in the Japanese Pharmacopoeia , and Liriope tubers cannot legally be used as Bakumondo in Japan. Ophiopogon plants can be distinguished clearly from Liriope by their fruit color and by the morphological characteristics of their flowers. However, the tubers of both species are greatly similar, making it very difficult to differentiate the two genera by the appearance of their tubers. We, therefore, investigated the most appropriate DNA regions to use for practical and accurate identification of Ophiopogon and Liriope tubers. The sequence of the gene for the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) was found to be suitable for discriminating Ophiopogon and Liriope tubers. The identification procedure was simplified using restriction enzyme digestion of the amplified rbcL fragment. The detection limit for Liriope contamination was estimated by performing the procedure using mixed samples of powdered Ophiopogon and Liriope tubers.