The Pharmacogenomics Knowledge Base (PharmGKB) [1] is a publicly available central resource for pharmacogenomics data and knowledge, which is being widely employed into clinical practice and thus requires using clinical terminologies. Hence, harmonizing PharmGKB drug data with well annotated drug terminologies will facilitate its integration with other related resources and support data representation, interpretation, and exchange within and across heterogeneous sources and applications. In this study, we extracted drug and drug class from PharmGKB, and mapped them to National Drug File Reference Terminology (NDF-RT) [2], which is integrated into RxNorm specified by U.S. Meaningful Use regulations. And the evaluated mapping results will be provided to PharmGKB for further investigation and collaboration.