The experimental horses were irradiated by a He-Ne laser beam on the palpebra tertja at a dosage of 3.5810J/cm3 per day lor 12 consecutive days. After irradiation, the content of IgG,IgM and IgA in serum were all increased significantly;the number of T-cell and B-cell in circulatory blood was increased significantly; the index of stimulation and counts perminuted in lymphocyte transformation test, and the activity of total complements in the serum increased significantly after irradiation.