This study investigated the antioxidant and immune enhancement activities of Artemisia argyi H. fermented by Lactobacillus plantarum. The fermented A. argyi H. ethanol extract increased scavenging activities of 1,1-diphenyl-2picrylhydrazyl (DPPH), 2,2'-azinobis-(3-ethylbenzothiazoline-6sulfonic acid) (ABTS + ), hydroxyl (•OH), and superoxide (O 2 -) radicals. Particularly, the ethanol extract of fermented A. argyi H. exhibited higher •OH and O 2 radical scavenging activities, compared with DPPH and ABTS + radical scavenging activities. To evaluate the immune enhancement effects of the fermented A. argyi H., mice were fed a normal diet supplemented the fermented A. argyi H. at concentrations of 1%, 2%, and 5%, respectively. The supplementation of fermented A. argyi H. dose-dependently increased splenocyte proliferation. In addition, mice fed with 5% fermented A. argyi H. showed enhanced proliferation of T-cells and B-cells, along with increased levels of interferon-γ, interleukin-10, and tumor necrosis factor-α, compared to the normal group. Furthermore, mice fed with fermented A. argyi H. exhibited an increase in prominent probiotics such as Akkermansia muciniphila and Lactobacillus in gut microbiota, compared to the normal group. This study suggests that fermented A. argyi H. with Lactobacillus plantarum could be used as a dietary antioxidant and immune enhancement agent.