An effective antimalaria constituent was ex-tracted from a traditional Chinese medicinal herb–Qinghao (Artemisia annua L); in 1972. It was named Qinghaosu¡. Accord-ing to the data from spectral analysis, X-ray dif-fraction analysis and chemical reaction it is a new type sesquiterpene lactone with a peroxy-group. Pharmacologic studies and clinical observations in every type of malarial infection show that Qinghaosu is a new type antimalaria drug with rapid action and low toxicity. It has direct pa-rasiticidal action on plasmodium in the ery-throcytic stage. The parasites in plasmodium vivac and plasmodium falciparum (including cerebral malaria and chloroquine-resistant falciparum malaria) especially in the areas of chlor0uine-resistant falciparum malaria were clear-ed more rapidly than that with chloroquine and quinine etc, it is ineffective in the tissue stage. In general the short term recurrence rate is higher with Ginghaosu than with chloroquine,