Bai Zhu (Atractylodes), the rhizome of Atractylodis macrocephalae, is a traditional Chinese herbal medicine. The present study was designed to evaluate the effects of oral administration of a water extract of Bai Zhu (Atractylodes) on the immune responses in mice immunized with the protein antigen ovalbumin (OVA). Forty-eight mice were divided into 6 groups of 8 animals each; 1 control group (saline solution) and 5 treatment groups (oral dose of 0.05 gm, 0.1 gm, 0.2 gm, 0.4 gm or 0.8 gm of Bai Zhu (Atractylodes) for 4 days). Animals were subcutaneously immunized with OVA (10 μg) in 0.89% saline solution on Day 5 and again 2 weeks later. Serum samples were collected 2 weeks after the second OVA injection, measuring OVA-specific IgG and the IgG subclasses, lymphocyte proliferation and IL-5 and IFN-γ production in splenocytes. Results indicated serum OVA-specific IgG titers and the IgG subclass responses were significantly enhanced in groups of mice receiving 0.1-0.8 gm Bai Zhu (Atractylodes) compared to the control group (p<0.05). Two weeks after the last immunization with OVA, splenic tissue was collected. Splenocyte proliferation in response to Concanavalin A and lipopolysaccharides was also significantly enhanced (p<0.05) in the treatment groups. Production of both IFN-γ and IL-5 by Con A-stimulated splenocytes was significantly higher in mice administered Bai Zhu (Atractylodes) at a dose of 0.2 gm orally than the control mice (p<0.05). Further study of Bai Zhu (Atractylodes) to evaluate its potential to improve the immune response to vaccines against infectious diseases is warranted.