Abstract: The experiment was conducted to access the effect of muscovy duck reovirusis alive vaccine on immune response and to explore the immune mechanism. After 1dayold muscovy ducks were immunized, the growth and development were observed, neutralization antibody in the sera, proliferation responses of the lymphocytes in the peripheral blood, thymus and bursa cells to ConA and LPS, Cytotoxic activity of cytotoxic T lymphocytes (CTL) were detected. The results showed that the growth and development of the immunized muscovy ducks were more than that of control group. The neutralization antibody began to increase until 35 days. Lymphocyte proliferation response to ConA in blood and thymus was enhanced differently in the immunized muscovy ducks, but response to LPS in blood and bursa weren’t changed differently. The cytotoxic activity of CTL in the immunized muscovy ducks was improved. So the muscovy duck reovirusis alive vaccine can improve the resistant ability of muscovy ducks to muscovy duck reovirus mainly by increasing cellular immunity．It laid theoretical basis on clinical application with muscovy duck alive vaccine.