The herbs of Orostachys japonicus (Crassulaceae) have been used to treat gastric cancer, gastric ulcer or hemorrhage. Flavonoid glycosides, mainly kaempferol (Kp)- and quercetin (Qc) glycosides, have been isolated from O. japonicus; however, no quantitative information on those flavonol glycosides and no peroxynitritescavenging activity of the Orostachys extracts have been reported. In this study, Kp- and Qc glycosides were qualitatively and quantitatively analyzed by high-performance liquid chromatography (HPLC) in eight Orostachys and a Meterostachys species including O. japonicas, O. margaritifolius, O. chongsunensis, O. minuta, O. ramosus, O. malacophylla, O. latiellipticus, O. iwarenge, O. iwarenge for. magnus, and Meterostachys sikokiana distributed or cultivated in Korea. Distinctively, O. margaritifolius contained two flavonol 3,7-di-O-glycosides of Kp 3,7-di-O-glucoside and Kp 3-rhamnosyl-7-glucoside, but O. japonicus had two flavonol 3-O-rutinosides, Kp 3-rutinoside and Qc 3-rutinoside. The three species of O. margaritifolius (24.36 mg/g MeOH extract), O. japonicus (21.28 mg/g), and O. minuta (19.50 mg/g) showed relatively higher flavonoid contents. The flavonol glycosides were analyzed using eight standard compounds (Kp, Qc, Qc 3-O-rhamnoside, Qc 3-O-glucoside, Kp 3- O-rutinoside, Qc 3-O-rutinoside, Kp 3-O-rhamnosyl-7-O-glucoside, Kp 3,7-di-O-glucoside). The present HPLC method was validated to verify the linearity, precision, and accuracy. In addition, the peroxynitrite-scavenging activity was also discussed.