Abstract: OBJECTIVE To determine the optimal harvest period of Artemisia annua as well as the optimal sampling time in its breeding. METHODS The banches of A.annua were cut in late vegetative stage, flower bud differentiation stage, full bud stage and flowering stage respectively from 15 plants randomly selected, and artemisinin contents of their extracted parts were measured, while 10 plants were cut and their yields extracted parts were measured in every developmental stage. Otherwise, five plants were cut in flower bud differentiation stage and full bud stage, and the yields and artemisinin contents of extracted parts of their first, second, third level branchs were measured respectively. RESULTS Artemisinin contents of extracted parts decreased gradually from late vegetative stage to flowering stage. The yields of extracted parts and artemisinin were the highest at full bud stage, then at the stage of flower bud, the third at flowering stage and the lowest at late vegetative stage. There was a significant positive correlation among the artemisinin contents in the extracted parts at different stages of the same single plant(r=0.494 4-0.791 1). The artemisinin contents in the extracted parts of different level branches of the same single plant at flower bud differentiation and full bud stage had no obvious difference, but the yields of artemisinin of each level branches differed significantly, and were in the order of the third>the second>the first. CONCLUSION The optimal harvest time of A. annua is young bud stage when the leaves of the third level branches full spread and the optimal sampling time is at late vegetative stage in its breeding.