Peroxynitrite (ONOO−) is one of cytotoxic species produced by the reaction between superoxide (•O2−) and nitric oxide (NO). The main aim of this study was to identify ONOO− scavenging constituents from herbs. Methanolic extracts derived from one hundred thirty eight herbs were screened out for their ONOO− scavenging activities. Twenty herbs showed excellent ONOO− scavenging activity in a dose dependent manner. Of them, Artemisia iwayomogi, which showed the highest activity, was fractioned with several solvents. The ONOO− scavenging activity of fractions was in order of ethyl acetate (EtOAc) > n‐butanol (BuOH) > dichloromethane (CH2Cl2) > water (H2O) fraction. The EtOAc and the n‐BuOH fractions were further purified to isolate active principles by column chromatography. Apigenin 7‐methylether (genkwanin), apigenin 7,4′‐di‐O methylether, jaceosidin, and scopoletin from the EtOAc fraction and chlorogenic acid, 2,4‐dihydroxy 6‐methoxy acetophenone 4‐O‐β‐D‐glucoside, quebrachitol, and scopolin from the n‐BuOH fraction were identified. The scavenging activities of chlorogenic acid (IC50 = 0.52 ± 0.04 µM), genkwanin (IC50 = 1.01 ± 0.10 µM), and scopoletin (IC50 = 1.03 ± 0.15 µM) were higher than or comparable to a well‐known ONOO− scavenger, penicillamine (IC50 = 1.76 ± 0.18 µM), suggesting that those compounds might be developed as effective ONOO− scavengers for, prevention of the ONOO−‐involved diseases. Copyright © 2004 John Wiley & Sons, Ltd.