Interleukin-6 (IL-6)/signal transducer and activator of transcription 3 (STAT3) signaling pathway plays critical roles in the development and progression of hepatocellular carcinoma (HCC). Artemisia capillaris (AC) has been widely used to treat various liver diseases including HCC as a herbal medicine. The effects of AC on IL-6/STAT3 signaling axis in HCC cells and subsequent anticancer activity of AC against HCC were analyzed using HCC cell lines and HBV W4P-LHB-expressing NIH3T3 cell line, which has been shown to gain tumorigenicity by activating IL-6/STAT3 signaling in our previous study. AC extract significantly suppressed the growth and colony formation of HCC cells. In addition, it inhibited the activation of STAT3 by IL-6 and subsequent synthesis of downstream molecules in HCC and W4P-NIH3T3 cells. Consequently, migration of cells was significantly suppressed by the AC extract. Collectively, the findings suggest that AC extract is capable of conferring various antitumor effects against HCC through the modulation of the IL-6/STAT3 pathway. The results provide a basis for the therapeutic use of AC in the treatment of HCC. Identification of the compound responsible for the effect may lead to the development of a novel anticancer agent against HCC.