d-3-Methoxy-17-methylmorphinan (Dextromethorphan, DXM), which is a structural analog of morphine and codeine, has been widely used as a non-narcotic antitussive agent. It is a safe drug in therapeutic dose and does not produce analgesic effects, while its enantiomer, l-3-methoxy-17-methylmorphinan called levomethorphan (LXM) is a potent narcotic analgesic. DXM has been widely abused in Korea due to its hallucinogenic effect in large doses; therefore, the health authorities have regulated its use as a psychotropic agent since 2003. As its abuse has been serious, a possibility that DXM would be smuggled into Korea has also increased. Moreover, it has been suspected that there was the possibility of the adulteration or substitution of DXM with LXM due to their chemical similarities. Therefore, it was necessary for us to establish the enantiomeric separation of DXM and LXM. In this study, a liquid chromatographic method using a chiral column capable of separating stereoisomers of DXM as well as analyzing the major metabolites of DXM, 3-methoxymorphinan, 3-hydroxymorphinan, and 17-hydroxymethylmorphinan was developed. The validation of a method was studied through repeatability of retention times. Using this method, 32 confiscated DXM samples were analyzed to identify the enantiomers of DXM. As a result, DXM was detected in all samples and there was no evidence of the adulteration or substitution of DXM with LXM. Nevertheless, the stereochemical analysis of DXM and LXM is important not only to identify starting materials for illegal drug manufacture but also to understand the trends of abused drugs.