Objective: To investigate the immunological function of a yeast expression system for thymosin α1(Tα1). Methods: A constructed Tα1 yeast expression system was used to investigate the immunological function of orally administered Tα1. Dried yeast containing three different concentration of Tα1 was fed to normal Balb/c mice and other Balb/c mice whose immunities were inhibited in advance by cyclophosphamide. Synthesized Tα1 peptide was used as positive control and dried yeast with empty plasmid was used as negative control. CD4+ and CD8+ levels were detected by flow cytometry assay. TNF-α IFN-γ IL-2, IL-6 and IL-10 levels were detected by liquid chip. Results: In normal Balb/c mice or immune inhibition Balb/c mice, CD8+ levels were significantly increased. Especially in immune inhibition Balb/c mice, CD8+ levels in synthesized Tα1 group (18.77％±4.72％),small dose group (13.48％±6.17％) and large dose group (22.74％±1.09％) were significantly higher than that in empty yeast control group (7.49％±2.14％). Conclusion: Orally administered Tα1 has its certain immunomodulatory function.