Abstract: The early flowering gene CONSTANS (CO) from Arabidopsis thaliana was transferred into Artemisia annua using the Agrobacterium tumefaciens-mediated transformation system. The plant expression vector pBICO was constructed by inserting the CO gene into the binary vector pBI121 under the control of CaMV 35S promoter. Analyses of PCR, PCR Southern blot, and Southern blot revealed that the transgenic plants contained the foreign CO gene. The results of RT-PCT and RT-PCR Southern blot suggested that the foreign CO gene had expressed at the transcriptional level. Although the flowering time of the CO transgenic plant was about 2 weeks earlier than that of the non-transgenic plant under short-day conditions, no significant difference in artemisinin content was found between the flowering transgenic plant and the non-flowering non-transgenic plant. These results show that the usually observed increase of artemisinin content before plant flowering under natural conditions is not a direct consequence of flowering itself, perhaps there is even no direct linkage between flowering and artemisinin biosynthesis.