We investigated the immunopharmacol. characteristics of the effects of Byakujutsu (Atractylodes rhizome) and Soujutsu (Atractylodes lancea rhizome) extracts, which are important ingredients of numerous traditional Japanese herbal medicines, on small intestinal intraepithelial lymphocytes. Both Byakujutsu and Soujutsu extracts increased the percentage of T cell receptor (TcR) γδ+ cells. Furthermore, Byakujutsu extract increased TcRαβ+ CD8α+ CD4+ cells, while Soujutsu extract increased the percentage of TcRαβ+CD4- cells. Byakujutsu extract increased the expression of mRNAs of FasL and perforin compared with the control and Soujutsu extract Byakujutsu extract inhibited the formation of interleukin-5 by Th1/Th2 cytokines, while Soujutsu extract enhanced the formation of interferon-γ. These findings suggest that Byakujutsu and Soujutsu extracts have different effects on small intestinal intraepithelial lymphocytes.